scripts/dic2markdown: tests/cases/dic2markdown_004.inp: WARNING, some data items of category 'diffrn_radiation_wavelength' are defined as looped while some are not -- category has to be split in order to be represented correctly in DDLm.
scripts/dic2markdown: tests/cases/dic2markdown_004.inp: WARNING, '_units_detail' is not defined for 'diffrn_source_take-off_angle'.
scripts/dic2markdown: tests/cases/dic2markdown_004.inp: WARNING, some data items of category 'exptl_crystal' are defined as looped while some are not -- category has to be split in order to be represented correctly in DDLm.
scripts/dic2markdown: tests/cases/dic2markdown_004.inp: WARNING, some data items of category 'space_group' are defined as looped while some are not -- category has to be split in order to be represented correctly in DDLm.
scripts/dic2markdown: tests/cases/dic2markdown_004.inp: WARNING, some data items of category 'space_group_symop' are defined as looped while some are not -- category has to be split in order to be represented correctly in DDLm.
scripts/dic2markdown: tests/cases/dic2markdown_004.inp: WARNING, some data items of category 'symmetry_equiv' are defined as looped while some are not -- category has to be split in order to be represented correctly in DDLm.
scripts/dic2markdown: tests/cases/dic2markdown_004.inp: WARNING, apparently DDL1 dictionary was encountered, converting it to DDLm; the conversion is experimental and may result in corruption or loss of dictionary data.
# CIF\_CORE

Version: 2.4 (2008-03-10)

## <a name="ATOM_SITE"></a>ATOM\_SITE

Data items in the ATOM\_SITE category record details about
 the atom sites in a crystal structure, such as the positional
 coordinates, atomic displacement parameters, and magnetic moments
 and directions.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
_atom_site_label
_atom_site_fract_x
_atom_site_fract_y
_atom_site_fract_z
_atom_site_U_iso_or_equiv
_atom_site_adp_type
_atom_site_calc_flag
_atom_site_calc_attached_atom
  O1   .4154(4)  .5699(1)  .3026(0)  .060(1)  Uani  ?    ?
  C2   .5630(5)  .5087(2)  .3246(1)  .060(2)  Uani  ?    ?
  C3   .5350(5)  .4920(2)  .3997(1)  .048(1)  Uani  ?    ?
  N4   .3570(3)  .5558(1)  .4167(0)  .039(1)  Uani  ?    ?
  C5   .3000(5)  .6122(2)  .3581(1)  .045(1)  Uani  ?    ?
  O21  .6958(5)  .4738(2)  .2874(1)  .090(2)  Uani  ?    ?
  C31  .4869(6)  .3929(2)  .4143(2)  .059(2)  Uani  ?    ?
 # - - - - data truncated for brevity - - - -
  H321C  .04(1)  .318(3)   .320(2)   .14000   Uiso  ?    ?
  H322A  .25(1)  .272(4)   .475(3)   .19000   Uiso  ?    ?
  H322B  .34976  .22118    .40954    .19000   Uiso  calc C322
  H322C  .08(1)  .234(4)   .397(3)   .19000   Uiso  ?    ?
</code></pre>
  </td><td>Example 1 - based on data set TOZ of Willis, Beckwith &amp; Tozer
            [Acta Cryst. (1991), C47, 2276-2277].
  </td></tr>
  <tr><td>
<pre><code>
loop_
_atom_site_aniso_label
_atom_site_aniso_B_11
_atom_site_aniso_B_22
_atom_site_aniso_B_33
_atom_site_aniso_B_12
_atom_site_aniso_B_13
_atom_site_aniso_B_23
_atom_site_aniso_type_symbol
 O1   .071(1) .076(1) .0342(9) .008(1)   .0051(9) -.0030(9) O
 C2   .060(2) .072(2) .047(1)  .002(2)   .013(1)  -.009(1)  C
 C3   .038(1) .060(2) .044(1)  .007(1)   .001(1)  -.005(1)  C
 N4   .037(1) .048(1) .0325(9) .0025(9)  .0011(9) -.0011(9) N
 C5   .043(1) .060(1) .032(1)  .001(1)  -.001(1)   .001(1)  C
 # - - - - data truncated for brevity - - - -
 O21  .094(2) .109(2) .068(1)  .023(2)   .038(1)  -.010(1)  O
 C51  .048(2) .059(2) .049(1)  .002(1)  -.000(1)   .007(1)  C
 C511 .048(2) .071(2) .097(3) -.008(2)  -.003(2)   .010(2)  C
 C512 .078(2) .083(2) .075(2)  .009(2)  -.005(2)   .033(2)  C
 C513 .074(2) .055(2) .075(2)  .004(2)   .001(2)  -.010(2)  C
 # - - - - data truncated for brevity - - - -
</code></pre>
  </td><td>Example 2 - based on data set TOZ of Willis, Beckwith &amp; Tozer
            [Acta Cryst. (1991), C47, 2276-2277].
  </td></tr>
  <tr><td>
<pre><code>
loop_
_atom_site_label
_atom_site_chemical_conn_number
_atom_site_fract_x
_atom_site_fract_y
_atom_site_fract_z
_atom_site_U_iso_or_equiv
 S1  1  0.74799(9)  -0.12482(11)  0.27574(9)  0.0742(3)
 S2  2  1.08535(10)  0.16131(9)   0.34061(9)  0.0741(3)
 N1  3  1.0650(2)   -0.1390(2)    0.2918(2)   0.0500(5)
 C1  4  0.9619(3)   -0.0522(3)    0.3009(2)   0.0509(6)
 # - - - - data truncated for brevity - - - -
</code></pre>
  </td><td>Example 3 - based on data set DPTD of Yamin, Suwandi, Fun, Sivakumar &amp;
            bin Shawkataly [Acta Cryst. (1996), C52, 951-953].
  </td></tr>
  <tr><td>
<pre><code>
loop_
 _atom_site_label                  # *_assembly &#39;M&#39; is a disordered methyl
 _atom_site_occupancy              # with configurations &#39;A&#39; and &#39;B&#39;:
 _atom_site_disorder_assembly      #
 _atom_site_disorder_group         #    H11B    H11A      H13B
                                   #      .      |      .
   C1     1      .       .              #        .    |    .
   H11A   .5     M       A              #          .  |  .
   H12A   .5     M       A              #             C1 &mdash;&mdash;&ndash;C2&mdash;
   H13A   .5     M       A              #           / .  \
   H11B   .5     M       B              #         /   .    \
   H12B   .5     M       B              #       /     .      \
   H13B   .5     M       B              #    H12A    H12B    H13A

</code></pre>
  </td><td>Example 4 - hypothetical example to illustrate the description of a
            disordered methyl group.
  </td></tr>
</table>
### <a name="_atom_site_adp_type"></a>\_atom\_site\_adp\_type

A standard code used to describe the type of atomic displacement
 parameters used for the site.

Values:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>Uani</td><td>anisotropic Uij</td></tr>
  <tr><td>Uiso</td><td>isotropic U</td></tr>
  <tr><td>Uovl</td><td>overall U</td></tr>
  <tr><td>Umpe</td><td>multipole expansion U</td></tr>
  <tr><td>Bani</td><td>anisotropic Bij</td></tr>
  <tr><td>Biso</td><td>isotropic B</td></tr>
  <tr><td>Bovl</td><td>overall B</td></tr>
</table>
### <a name="_atom_site_aniso_B_11"></a>\_atom\_site\_aniso\_B\_11

These are the standard anisotropic atomic displacement
 components in angstroms squared which appear in the 
 structure-factor term

 T = exp{-(1/4) sum~i~ [ sum~j~ (B^ij^ h~i~ h~j~ a\*~i~ a\*~j~) ] }

 h = the Miller indices
 a\* = the reciprocal-space cell lengths

 The unique elements of the real symmetric matrix are
 entered by row.

 The IUCr Commission on Nomenclature recommends against the use
 of B for reporting atomic displacement parameters. U, being
 directly proportional to B, is preferred.

Units: angstroms\_squared

### <a name="_atom_site_aniso_B_12"></a>\_atom\_site\_aniso\_B\_12

These are the standard anisotropic atomic displacement
 components in angstroms squared which appear in the 
 structure-factor term

 T = exp{-(1/4) sum~i~ [ sum~j~ (B^ij^ h~i~ h~j~ a\*~i~ a\*~j~) ] }

 h = the Miller indices
 a\* = the reciprocal-space cell lengths

 The unique elements of the real symmetric matrix are
 entered by row.

 The IUCr Commission on Nomenclature recommends against the use
 of B for reporting atomic displacement parameters. U, being
 directly proportional to B, is preferred.

Units: angstroms\_squared

### <a name="_atom_site_aniso_B_13"></a>\_atom\_site\_aniso\_B\_13

These are the standard anisotropic atomic displacement
 components in angstroms squared which appear in the 
 structure-factor term

 T = exp{-(1/4) sum~i~ [ sum~j~ (B^ij^ h~i~ h~j~ a\*~i~ a\*~j~) ] }

 h = the Miller indices
 a\* = the reciprocal-space cell lengths

 The unique elements of the real symmetric matrix are
 entered by row.

 The IUCr Commission on Nomenclature recommends against the use
 of B for reporting atomic displacement parameters. U, being
 directly proportional to B, is preferred.

Units: angstroms\_squared

### <a name="_atom_site_aniso_B_22"></a>\_atom\_site\_aniso\_B\_22

These are the standard anisotropic atomic displacement
 components in angstroms squared which appear in the 
 structure-factor term

 T = exp{-(1/4) sum~i~ [ sum~j~ (B^ij^ h~i~ h~j~ a\*~i~ a\*~j~) ] }

 h = the Miller indices
 a\* = the reciprocal-space cell lengths

 The unique elements of the real symmetric matrix are
 entered by row.

 The IUCr Commission on Nomenclature recommends against the use
 of B for reporting atomic displacement parameters. U, being
 directly proportional to B, is preferred.

Units: angstroms\_squared

### <a name="_atom_site_aniso_B_23"></a>\_atom\_site\_aniso\_B\_23

These are the standard anisotropic atomic displacement
 components in angstroms squared which appear in the 
 structure-factor term

 T = exp{-(1/4) sum~i~ [ sum~j~ (B^ij^ h~i~ h~j~ a\*~i~ a\*~j~) ] }

 h = the Miller indices
 a\* = the reciprocal-space cell lengths

 The unique elements of the real symmetric matrix are
 entered by row.

 The IUCr Commission on Nomenclature recommends against the use
 of B for reporting atomic displacement parameters. U, being
 directly proportional to B, is preferred.

Units: angstroms\_squared

### <a name="_atom_site_aniso_B_33"></a>\_atom\_site\_aniso\_B\_33

These are the standard anisotropic atomic displacement
 components in angstroms squared which appear in the 
 structure-factor term

 T = exp{-(1/4) sum~i~ [ sum~j~ (B^ij^ h~i~ h~j~ a\*~i~ a\*~j~) ] }

 h = the Miller indices
 a\* = the reciprocal-space cell lengths

 The unique elements of the real symmetric matrix are
 entered by row.

 The IUCr Commission on Nomenclature recommends against the use
 of B for reporting atomic displacement parameters. U, being
 directly proportional to B, is preferred.

Units: angstroms\_squared

### <a name="_atom_site_aniso_label"></a>\_atom\_site\_aniso\_label

Anisotropic atomic displacement parameters are usually looped in
 a separate list. If this is the case, this code must match the
 [\_atom\_site\_label](#_atom_site_label) of the associated atom in the atom coordinate
 list and conform with the same rules described in
 [\_atom\_site\_label](#_atom_site_label).

### <a name="_atom_site_aniso_ratio"></a>\_atom\_site\_aniso\_ratio

Ratio of the maximum to minimum principal axes of
 displacement (thermal) ellipsoids.

### <a name="_atom_site_aniso_type_symbol"></a>\_atom\_site\_aniso\_type\_symbol

This [\_atom\_type\_symbol](#_atom_type_symbol) code links the anisotropic atom
 parameters to the atom-type data associated with this site and
 must match one of the [\_atom\_type\_symbol](#_atom_type_symbol) codes in this list.

### <a name="_atom_site_aniso_U_11"></a>\_atom\_site\_aniso\_U\_11

These are the standard anisotropic atomic displacement
 components in angstroms squared which appear in the
 structure-factor term

 T = exp{-2pi^2^ sum~i~ [sum~j~ (U^ij^ h~i~ h~j~ a\*~i~ a\*~j~) ] }

 h = the Miller indices
 a\* = the reciprocal-space cell lengths

 The unique elements of the real symmetric matrix are
 entered by row.

Units: angstroms\_squared

### <a name="_atom_site_aniso_U_12"></a>\_atom\_site\_aniso\_U\_12

These are the standard anisotropic atomic displacement
 components in angstroms squared which appear in the
 structure-factor term

 T = exp{-2pi^2^ sum~i~ [sum~j~ (U^ij^ h~i~ h~j~ a\*~i~ a\*~j~) ] }

 h = the Miller indices
 a\* = the reciprocal-space cell lengths

 The unique elements of the real symmetric matrix are
 entered by row.

Units: angstroms\_squared

### <a name="_atom_site_aniso_U_13"></a>\_atom\_site\_aniso\_U\_13

These are the standard anisotropic atomic displacement
 components in angstroms squared which appear in the
 structure-factor term

 T = exp{-2pi^2^ sum~i~ [sum~j~ (U^ij^ h~i~ h~j~ a\*~i~ a\*~j~) ] }

 h = the Miller indices
 a\* = the reciprocal-space cell lengths

 The unique elements of the real symmetric matrix are
 entered by row.

Units: angstroms\_squared

### <a name="_atom_site_aniso_U_22"></a>\_atom\_site\_aniso\_U\_22

These are the standard anisotropic atomic displacement
 components in angstroms squared which appear in the
 structure-factor term

 T = exp{-2pi^2^ sum~i~ [sum~j~ (U^ij^ h~i~ h~j~ a\*~i~ a\*~j~) ] }

 h = the Miller indices
 a\* = the reciprocal-space cell lengths

 The unique elements of the real symmetric matrix are
 entered by row.

Units: angstroms\_squared

### <a name="_atom_site_aniso_U_23"></a>\_atom\_site\_aniso\_U\_23

These are the standard anisotropic atomic displacement
 components in angstroms squared which appear in the
 structure-factor term

 T = exp{-2pi^2^ sum~i~ [sum~j~ (U^ij^ h~i~ h~j~ a\*~i~ a\*~j~) ] }

 h = the Miller indices
 a\* = the reciprocal-space cell lengths

 The unique elements of the real symmetric matrix are
 entered by row.

Units: angstroms\_squared

### <a name="_atom_site_aniso_U_33"></a>\_atom\_site\_aniso\_U\_33

These are the standard anisotropic atomic displacement
 components in angstroms squared which appear in the
 structure-factor term

 T = exp{-2pi^2^ sum~i~ [sum~j~ (U^ij^ h~i~ h~j~ a\*~i~ a\*~j~) ] }

 h = the Miller indices
 a\* = the reciprocal-space cell lengths

 The unique elements of the real symmetric matrix are
 entered by row.

Units: angstroms\_squared

### <a name="_atom_site_attached_hydrogens"></a>\_atom\_site\_attached\_hydrogens

The number of hydrogen atoms attached to the atom at this site
 excluding any hydrogen atoms for which coordinates (measured or
 calculated) are given.

Default value: '0'

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
2
  </td><td>water oxygen
  </td></tr>
  <tr><td>
1
  </td><td>hydroxyl oxygen
  </td></tr>
  <tr><td>
4
  </td><td>ammonium nitrogen
  </td></tr>
</table>
### <a name="_atom_site_B_equiv_geom_mean"></a>\_atom\_site\_B\_equiv\_geom\_mean

Equivalent isotropic atomic displacement parameter, B(equiv),
 in angstroms squared, calculated as the geometric mean of
 the anisotropic atomic displacement parameters.

 B(equiv) = (B~i~ B~j~ B~k~)^1/3^

 B~n~  = the principal components of the orthogonalized B^ij^

 The IUCr Commission on Nomenclature recommends against the use
 of B for reporting atomic displacement parameters. U, being
 directly proportional to B, is preferred.

Units: angstroms\_squared

### <a name="_atom_site_B_iso_or_equiv"></a>\_atom\_site\_B\_iso\_or\_equiv

Isotropic atomic displacement parameter, or equivalent isotropic
 atomic displacement parameter, B(equiv), in angstroms squared,
 calculated from anisotropic displacement components.

 B(equiv) = (1/3) sum~i~[sum~j~(B^ij^ a\*~i~ a\*~j~ a~i~ a~j~)]

 a     = the real-space cell lengths
 a\*    = the reciprocal-space cell lengths
 B^ij^ = 8 pi^2^ U^ij^

 Ref: Fischer, R. X. &amp; Tillmanns, E. (1988). Acta Cryst. C44,
      775-776.

 The IUCr Commission on Nomenclature recommends against the use
 of B for reporting atomic displacement parameters. U, being
 directly proportional to B, is preferred.

Units: angstroms\_squared

### <a name="_atom_site_calc_attached_atom"></a>\_atom\_site\_calc\_attached\_atom

The [\_atom\_site\_label](#_atom_site_label) of the atom site to which the &#39;geometry-
 calculated&#39; atom site is attached.

Default value: '.'

### <a name="_atom_site_calc_flag"></a>\_atom\_site\_calc\_flag

A standard code to signal whether the site coordinates have been
 determined from the intensities or calculated from the geometry
 of surrounding sites, or have been assigned dummy coordinates.
 The abbreviation &#39;c&#39; may be used in place of &#39;calc&#39;.

Values:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>d</td><td>determined from diffraction measurements</td></tr>
  <tr><td>calc</td><td>calculated from molecular geometry</td></tr>
  <tr><td>c</td><td>abbreviation for &quot;calc&quot;</td></tr>
  <tr><td>dum</td><td>dummy site with meaningless coordinates</td></tr>
</table>
Default value: 'd'

### <a name="_atom_site_Cartn_x"></a>\_atom\_site\_Cartn\_x

The atom-site coordinates in angstroms specified according to a
 set of orthogonal Cartesian axes related to the cell axes as
 specified by the [\_atom\_sites\_Cartn\_transform\_axes](#_atom_sites_Cartn_transform_axes) description.

Units: angstroms

### <a name="_atom_site_Cartn_y"></a>\_atom\_site\_Cartn\_y

The atom-site coordinates in angstroms specified according to a
 set of orthogonal Cartesian axes related to the cell axes as
 specified by the [\_atom\_sites\_Cartn\_transform\_axes](#_atom_sites_Cartn_transform_axes) description.

Units: angstroms

### <a name="_atom_site_Cartn_z"></a>\_atom\_site\_Cartn\_z

The atom-site coordinates in angstroms specified according to a
 set of orthogonal Cartesian axes related to the cell axes as
 specified by the [\_atom\_sites\_Cartn\_transform\_axes](#_atom_sites_Cartn_transform_axes) description.

Units: angstroms

### <a name="_atom_site_chemical_conn_number"></a>\_atom\_site\_chemical\_conn\_number

This number links an atom site to the chemical connectivity list.
 It must match a number specified by [\_chemical\_conn\_atom\_number](#_chemical_conn_atom_number).

### <a name="_atom_site_constraints"></a>\_atom\_site\_constraints

A description of the constraints applied to parameters at this
 site during refinement. See also [\_atom\_site\_refinement\_flags](#_atom_site_refinement_flags)
 and [\_refine\_ls\_number\_constraints](#_refine_ls_number_constraints).

Default value: '.'

### <a name="_atom_site_description"></a>\_atom\_site\_description

A description of special aspects of this site. See also
 [\_atom\_site\_refinement\_flags](#_atom_site_refinement_flags).

### <a name="_atom_site_disorder_assembly"></a>\_atom\_site\_disorder\_assembly

A code which identifies a cluster of atoms that show long-range
 positional disorder but are locally ordered. Within each such
 cluster of atoms, [\_atom\_site\_disorder\_group](#_atom_site_disorder_group) is used to identify
 the sites that are simultaneously occupied. This field is only
 needed if there is more than one cluster of disordered atoms
 showing independent local order.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
A
  </td><td>disordered methyl assembly with groups 1 and 2
  </td></tr>
  <tr><td>
B
  </td><td>disordered sites related by a mirror
  </td></tr>
  <tr><td>
S
  </td><td>disordered sites independent of symmetry
  </td></tr>
</table>
### <a name="_atom_site_disorder_group"></a>\_atom\_site\_disorder\_group

A code which identifies a group of positionally disordered atom
 sites that are locally simultaneously occupied. Atoms that are
 positionally disordered over two or more sites (e.g. the hydrogen
 atoms of a methyl group that exists in two orientations) can
 be assigned to two or more groups. Sites belonging to the same
 group are simultaneously occupied, but those belonging to
 different groups are not. A minus prefix (e.g. &quot;-1&quot;) is used to
 indicate sites disordered about a special position.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
1
  </td><td>unique disordered site in group 1
  </td></tr>
  <tr><td>
2
  </td><td>unique disordered site in group 2
  </td></tr>
  <tr><td>
-1
  </td><td>symmetry-independent disordered site
  </td></tr>
</table>
### <a name="_atom_site_fract_x"></a>\_atom\_site\_fract\_x

Atom-site coordinates as fractions of the \_cell\_length\_ values.

### <a name="_atom_site_fract_y"></a>\_atom\_site\_fract\_y

Atom-site coordinates as fractions of the \_cell\_length\_ values.

### <a name="_atom_site_fract_z"></a>\_atom\_site\_fract\_z

Atom-site coordinates as fractions of the \_cell\_length\_ values.

### <a name="_atom_site_label"></a>\_atom\_site\_label

The [\_atom\_site\_label](#_atom_site_label) is a unique identifier for a particular site
 in the crystal. This code is made up of a sequence of up to seven
 components, \_atom\_site\_label\_component\_0 to \*\_6, which may be
 specified as separate data items. Component 0 usually matches one
 of the specified [\_atom\_type\_symbol](#_atom_type_symbol) codes. This is not mandatory
 if an [\_atom\_site\_type\_symbol](#_atom_site_type_symbol) item is included in the atom-site
 list. The [\_atom\_site\_type\_symbol](#_atom_site_type_symbol) always takes precedence over
 an [\_atom\_site\_label](#_atom_site_label) in the identification of the atom type. The
 label components 1 to 6 are optional, and normally only
 components 0 and 1 are used. Note that components 0 and 1 are
 concatenated, while all other components, if specified, are
 separated by an underscore. Underscores are
 only used if higher-order components exist. If an intermediate
 component is not used, it may be omitted provided the underscore
 separators are inserted. For example, the label &#39;C233\_\_ggg&#39; is
 acceptable and represents the components C, 233, &#39;&#39; and ggg.
 Different labels may have a different number of components.

### <a name="_atom_site_label_component_0"></a>\_atom\_site\_label\_component\_0

Component 0 is normally a code which matches identically with
 one of the [\_atom\_type\_symbol](#_atom_type_symbol) codes. If this is the case, then the
 rules governing the [\_atom\_type\_symbol](#_atom_type_symbol) code apply. If, however,
 the data item [\_atom\_site\_type\_symbol](#_atom_site_type_symbol) is also specified in the
 atom-site list, component 0 need not match this symbol or adhere
 to any of the [\_atom\_type\_symbol](#_atom_type_symbol) rules.
 Component 1 is referred to as the &quot;atom number&quot;. When component 0
 is the atom-type code, it is used to number the sites with the
 same atom type. This component code must start with at least one
 digit which is not followed by a + or - sign (to distinguish it
 from the component 0 rules).
 Components 2 to 6 contain the identifier, residue, sequence,
 asymmetry identifier and alternate codes, respectively. These
 codes may be composed of any characters except an underscore.

### <a name="_atom_site_label_component_1"></a>\_atom\_site\_label\_component\_1

Component 0 is normally a code which matches identically with
 one of the [\_atom\_type\_symbol](#_atom_type_symbol) codes. If this is the case, then the
 rules governing the [\_atom\_type\_symbol](#_atom_type_symbol) code apply. If, however,
 the data item [\_atom\_site\_type\_symbol](#_atom_site_type_symbol) is also specified in the
 atom-site list, component 0 need not match this symbol or adhere
 to any of the [\_atom\_type\_symbol](#_atom_type_symbol) rules.
 Component 1 is referred to as the &quot;atom number&quot;. When component 0
 is the atom-type code, it is used to number the sites with the
 same atom type. This component code must start with at least one
 digit which is not followed by a + or - sign (to distinguish it
 from the component 0 rules).
 Components 2 to 6 contain the identifier, residue, sequence,
 asymmetry identifier and alternate codes, respectively. These
 codes may be composed of any characters except an underscore.

### <a name="_atom_site_label_component_2"></a>\_atom\_site\_label\_component\_2

Component 0 is normally a code which matches identically with
 one of the [\_atom\_type\_symbol](#_atom_type_symbol) codes. If this is the case, then the
 rules governing the [\_atom\_type\_symbol](#_atom_type_symbol) code apply. If, however,
 the data item [\_atom\_site\_type\_symbol](#_atom_site_type_symbol) is also specified in the
 atom-site list, component 0 need not match this symbol or adhere
 to any of the [\_atom\_type\_symbol](#_atom_type_symbol) rules.
 Component 1 is referred to as the &quot;atom number&quot;. When component 0
 is the atom-type code, it is used to number the sites with the
 same atom type. This component code must start with at least one
 digit which is not followed by a + or - sign (to distinguish it
 from the component 0 rules).
 Components 2 to 6 contain the identifier, residue, sequence,
 asymmetry identifier and alternate codes, respectively. These
 codes may be composed of any characters except an underscore.

### <a name="_atom_site_label_component_3"></a>\_atom\_site\_label\_component\_3

Component 0 is normally a code which matches identically with
 one of the [\_atom\_type\_symbol](#_atom_type_symbol) codes. If this is the case, then the
 rules governing the [\_atom\_type\_symbol](#_atom_type_symbol) code apply. If, however,
 the data item [\_atom\_site\_type\_symbol](#_atom_site_type_symbol) is also specified in the
 atom-site list, component 0 need not match this symbol or adhere
 to any of the [\_atom\_type\_symbol](#_atom_type_symbol) rules.
 Component 1 is referred to as the &quot;atom number&quot;. When component 0
 is the atom-type code, it is used to number the sites with the
 same atom type. This component code must start with at least one
 digit which is not followed by a + or - sign (to distinguish it
 from the component 0 rules).
 Components 2 to 6 contain the identifier, residue, sequence,
 asymmetry identifier and alternate codes, respectively. These
 codes may be composed of any characters except an underscore.

### <a name="_atom_site_label_component_4"></a>\_atom\_site\_label\_component\_4

Component 0 is normally a code which matches identically with
 one of the [\_atom\_type\_symbol](#_atom_type_symbol) codes. If this is the case, then the
 rules governing the [\_atom\_type\_symbol](#_atom_type_symbol) code apply. If, however,
 the data item [\_atom\_site\_type\_symbol](#_atom_site_type_symbol) is also specified in the
 atom-site list, component 0 need not match this symbol or adhere
 to any of the [\_atom\_type\_symbol](#_atom_type_symbol) rules.
 Component 1 is referred to as the &quot;atom number&quot;. When component 0
 is the atom-type code, it is used to number the sites with the
 same atom type. This component code must start with at least one
 digit which is not followed by a + or - sign (to distinguish it
 from the component 0 rules).
 Components 2 to 6 contain the identifier, residue, sequence,
 asymmetry identifier and alternate codes, respectively. These
 codes may be composed of any characters except an underscore.

### <a name="_atom_site_label_component_5"></a>\_atom\_site\_label\_component\_5

Component 0 is normally a code which matches identically with
 one of the [\_atom\_type\_symbol](#_atom_type_symbol) codes. If this is the case, then the
 rules governing the [\_atom\_type\_symbol](#_atom_type_symbol) code apply. If, however,
 the data item [\_atom\_site\_type\_symbol](#_atom_site_type_symbol) is also specified in the
 atom-site list, component 0 need not match this symbol or adhere
 to any of the [\_atom\_type\_symbol](#_atom_type_symbol) rules.
 Component 1 is referred to as the &quot;atom number&quot;. When component 0
 is the atom-type code, it is used to number the sites with the
 same atom type. This component code must start with at least one
 digit which is not followed by a + or - sign (to distinguish it
 from the component 0 rules).
 Components 2 to 6 contain the identifier, residue, sequence,
 asymmetry identifier and alternate codes, respectively. These
 codes may be composed of any characters except an underscore.

### <a name="_atom_site_label_component_6"></a>\_atom\_site\_label\_component\_6

Component 0 is normally a code which matches identically with
 one of the [\_atom\_type\_symbol](#_atom_type_symbol) codes. If this is the case, then the
 rules governing the [\_atom\_type\_symbol](#_atom_type_symbol) code apply. If, however,
 the data item [\_atom\_site\_type\_symbol](#_atom_site_type_symbol) is also specified in the
 atom-site list, component 0 need not match this symbol or adhere
 to any of the [\_atom\_type\_symbol](#_atom_type_symbol) rules.
 Component 1 is referred to as the &quot;atom number&quot;. When component 0
 is the atom-type code, it is used to number the sites with the
 same atom type. This component code must start with at least one
 digit which is not followed by a + or - sign (to distinguish it
 from the component 0 rules).
 Components 2 to 6 contain the identifier, residue, sequence,
 asymmetry identifier and alternate codes, respectively. These
 codes may be composed of any characters except an underscore.

### <a name="_atom_site_occupancy"></a>\_atom\_site\_occupancy

The fraction of the atom type present at this site.
 The sum of the occupancies of all the atom types at this site
 may not significantly exceed 1.0 unless it is a dummy site. The
 value must lie in the 99.97% Gaussian confidence interval
 -3u =&lt; x =&lt; 1 + 3u. The \_enumeration\_range of 0.0:1.0 is thus
 correctly interpreted as meaning (0.0 - 3u) =&lt; x =&lt; (1.0 + 3u).

Default value: '1.0'

### <a name="_atom_site_refinement_flags"></a>\_atom\_site\_refinement\_flags

A concatenated series of single-letter codes which indicate the
 refinement restraints or constraints applied to this site.  This
 item should not be used.  It has been replaced by
 [\_atom\_site\_refinement\_flags\_posn](#_atom_site_refinement_flags_posn), \*\_adp and \*\_occupancy. It is
 retained in this dictionary only to provide compatibility with
 legacy CIFs.

Values:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>.</td><td>no refinement constraints</td></tr>
  <tr><td>S</td><td>special-position constraint on site</td></tr>
  <tr><td>G</td><td>rigid-group refinement of site</td></tr>
  <tr><td>R</td><td>riding-atom site attached to non-riding atom</td></tr>
  <tr><td>D</td><td>distance or angle restraint on site</td></tr>
  <tr><td>T</td><td>thermal displacement constraints</td></tr>
  <tr><td>U</td><td>Uiso or Uij restraint (rigid bond)</td></tr>
  <tr><td>P</td><td>partial occupancy constraint</td></tr>
</table>
### <a name="_atom_site_refinement_flags_adp"></a>\_atom\_site\_refinement\_flags\_adp

A code which indicates the refinement restraints or constraints
 applied to the atomic displacement parameters of this site.

Values:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>.</td><td>no constraints on atomic displacement parameters</td></tr>
  <tr><td>T</td><td>special-position constraints on atomic displacement parameters</td></tr>
  <tr><td>U</td><td>Uiso or Uij restraint (rigid bond)</td></tr>
  <tr><td>TU</td><td>both constraints applied</td></tr>
</table>
### <a name="_atom_site_refinement_flags_occupancy"></a>\_atom\_site\_refinement\_flags\_occupancy

A code which indicates that refinement restraints or
 constraints were applied to the occupancy of this site.

Values:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>.</td><td>no constraints on site-occupancy parameters</td></tr>
  <tr><td>P</td><td>site-occupancy constraint</td></tr>
</table>
### <a name="_atom_site_refinement_flags_posn"></a>\_atom\_site\_refinement\_flags\_posn

A code which indicates the refinement restraints or constraints
 applied to the positional coordinates of this site.

Values:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>.</td><td>no constraints on  positional coordinates</td></tr>
  <tr><td>D</td><td>distance or angle restraint on positional coordinates</td></tr>
  <tr><td>G</td><td>rigid-group refinement of positional coordinates</td></tr>
  <tr><td>R</td><td>riding-atom site attached to non-riding atom</td></tr>
  <tr><td>S</td><td>special-position constraint on positional coordinates</td></tr>
  <tr><td>DG</td><td>combination of the above constraints</td></tr>
  <tr><td>DR</td><td>combination of the above constraints</td></tr>
  <tr><td>DS</td><td>combination of the above constraints</td></tr>
  <tr><td>GR</td><td>combination of the above constraints</td></tr>
  <tr><td>GS</td><td>combination of the above constraints</td></tr>
  <tr><td>RS</td><td>combination of the above constraints</td></tr>
  <tr><td>DGR</td><td>combination of the above constraints</td></tr>
  <tr><td>DGS</td><td>combination of the above constraints</td></tr>
  <tr><td>DRS</td><td>combination of the above constraints</td></tr>
  <tr><td>GRS</td><td>combination of the above constraints</td></tr>
  <tr><td>DGRS</td><td>combination of the above constraints</td></tr>
</table>
### <a name="_atom_site_restraints"></a>\_atom\_site\_restraints

A description of restraints applied to specific parameters at
 this site during refinement. See also [\_atom\_site\_refinement\_flags](#_atom_site_refinement_flags)
 and [\_refine\_ls\_number\_restraints](#_refine_ls_number_restraints).

### <a name="_atom_site_symmetry_multiplicity"></a>\_atom\_site\_symmetry\_multiplicity

The multiplicity of a site due to the space-group symmetry as
 given in International Tables for Crystallography Vol. A (2002).

### <a name="_atom_site_thermal_displace_type"></a>\_atom\_site\_thermal\_displace\_type

A standard code used to describe the type of atomic displacement
 parameters used for the site.

Values:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>Uani</td><td>anisotropic Uij</td></tr>
  <tr><td>Uiso</td><td>isotropic U</td></tr>
  <tr><td>Uovl</td><td>overall U</td></tr>
  <tr><td>Umpe</td><td>multipole expansion U</td></tr>
  <tr><td>Bani</td><td>anisotropic Bij</td></tr>
  <tr><td>Biso</td><td>isotropic B</td></tr>
  <tr><td>Bovl</td><td>overall B</td></tr>
</table>
### <a name="_atom_site_type_symbol"></a>\_atom\_site\_type\_symbol

A code to identify the atom species (singular or plural)
 occupying this site.
 This code must match a corresponding [\_atom\_type\_symbol](#_atom_type_symbol). The
 specification of this code is optional if component 0 of the
 [\_atom\_site\_label](#_atom_site_label) is used for this purpose. See [\_atom\_type\_symbol](#_atom_type_symbol).

### <a name="_atom_site_U_equiv_geom_mean"></a>\_atom\_site\_U\_equiv\_geom\_mean

Equivalent isotropic atomic displacement parameter, U(equiv),
 in angstroms squared, calculated as the geometric mean of
 the anisotropic atomic displacement parameters.

 U(equiv) = (U~i~ U~j~ U~k~)^1/3^

 U~n~  = the principal components of the orthogonalized U^ij^

Units: angstroms\_squared

### <a name="_atom_site_U_iso_or_equiv"></a>\_atom\_site\_U\_iso\_or\_equiv

Isotropic atomic displacement parameter, or equivalent isotropic
 atomic  displacement parameter, U(equiv), in angstroms squared,
 calculated from anisotropic atomic displacement  parameters.

 U(equiv) = (1/3) sum~i~[sum~j~(U^ij^ a\*~i~ a\*~j~ a~i~ a~j~)]

 a     = the real-space cell lengths
 a\*    = the reciprocal-space cell lengths

 Ref: Fischer, R. X. &amp; Tillmanns, E. (1988). Acta Cryst. C44,
      775-776.

Units: angstroms\_squared

### <a name="_atom_site_Wyckoff_symbol"></a>\_atom\_site\_Wyckoff\_symbol

The Wyckoff symbol (letter) as listed in the space-group tables
 of International Tables for Crystallography Vol. A (2002).

## <a name="ATOM_SITES"></a>ATOM\_SITES

Data items in the ATOM\_SITES category record details about
 the crystallographic cell and cell transformations, which are
 common to all atom sites.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
_atom_sites_Cartn_transform_axes
      &#39;c along z, astar along x, b along y&#39;

_atom_sites_Cartn_tran_matrix_11    58.39
_atom_sites_Cartn_tran_matrix_12     0.00
_atom_sites_Cartn_tran_matrix_13     0.00
_atom_sites_Cartn_tran_matrix_21     0.00
_atom_sites_Cartn_tran_matrix_22    86.70
_atom_sites_Cartn_tran_matrix_23     0.00
_atom_sites_Cartn_tran_matrix_31     0.00
_atom_sites_Cartn_tran_matrix_32     0.00
_atom_sites_Cartn_tran_matrix_33    46.27

</code></pre>
  </td><td>Example 1 - based on PDB entry 5HVP and laboratory records for the
            structure corresponding to PDB entry 5HVP.
  </td></tr>
</table>
### <a name="_atom_sites_Cartn_tran_matrix_11"></a>\_atom\_sites\_Cartn\_tran\_matrix\_11

Matrix elements used to transform fractional coordinates in
 the ATOM\_SITE category to Cartesian  coordinates. The axial
 alignments of this transformation are described in
 [\_atom\_sites\_Cartn\_transform\_axes](#_atom_sites_Cartn_transform_axes). The 3 x 1 translation is
 defined in \_atom\_sites\_Cartn\_tran\_vector\_.
   x&#39;                   |11 12 13|      x                  | 1 |
 ( y&#39; ) Cartesian   =   |21 22 23|    ( y ) fractional  +  | 2 |
   z&#39;                   |31 32 33|      z                  | 3 |

### <a name="_atom_sites_Cartn_tran_matrix_12"></a>\_atom\_sites\_Cartn\_tran\_matrix\_12

Matrix elements used to transform fractional coordinates in
 the ATOM\_SITE category to Cartesian  coordinates. The axial
 alignments of this transformation are described in
 [\_atom\_sites\_Cartn\_transform\_axes](#_atom_sites_Cartn_transform_axes). The 3 x 1 translation is
 defined in \_atom\_sites\_Cartn\_tran\_vector\_.
   x&#39;                   |11 12 13|      x                  | 1 |
 ( y&#39; ) Cartesian   =   |21 22 23|    ( y ) fractional  +  | 2 |
   z&#39;                   |31 32 33|      z                  | 3 |

### <a name="_atom_sites_Cartn_tran_matrix_13"></a>\_atom\_sites\_Cartn\_tran\_matrix\_13

Matrix elements used to transform fractional coordinates in
 the ATOM\_SITE category to Cartesian  coordinates. The axial
 alignments of this transformation are described in
 [\_atom\_sites\_Cartn\_transform\_axes](#_atom_sites_Cartn_transform_axes). The 3 x 1 translation is
 defined in \_atom\_sites\_Cartn\_tran\_vector\_.
   x&#39;                   |11 12 13|      x                  | 1 |
 ( y&#39; ) Cartesian   =   |21 22 23|    ( y ) fractional  +  | 2 |
   z&#39;                   |31 32 33|      z                  | 3 |

### <a name="_atom_sites_Cartn_tran_matrix_21"></a>\_atom\_sites\_Cartn\_tran\_matrix\_21

Matrix elements used to transform fractional coordinates in
 the ATOM\_SITE category to Cartesian  coordinates. The axial
 alignments of this transformation are described in
 [\_atom\_sites\_Cartn\_transform\_axes](#_atom_sites_Cartn_transform_axes). The 3 x 1 translation is
 defined in \_atom\_sites\_Cartn\_tran\_vector\_.
   x&#39;                   |11 12 13|      x                  | 1 |
 ( y&#39; ) Cartesian   =   |21 22 23|    ( y ) fractional  +  | 2 |
   z&#39;                   |31 32 33|      z                  | 3 |

### <a name="_atom_sites_Cartn_tran_matrix_22"></a>\_atom\_sites\_Cartn\_tran\_matrix\_22

Matrix elements used to transform fractional coordinates in
 the ATOM\_SITE category to Cartesian  coordinates. The axial
 alignments of this transformation are described in
 [\_atom\_sites\_Cartn\_transform\_axes](#_atom_sites_Cartn_transform_axes). The 3 x 1 translation is
 defined in \_atom\_sites\_Cartn\_tran\_vector\_.
   x&#39;                   |11 12 13|      x                  | 1 |
 ( y&#39; ) Cartesian   =   |21 22 23|    ( y ) fractional  +  | 2 |
   z&#39;                   |31 32 33|      z                  | 3 |

### <a name="_atom_sites_Cartn_tran_matrix_23"></a>\_atom\_sites\_Cartn\_tran\_matrix\_23

Matrix elements used to transform fractional coordinates in
 the ATOM\_SITE category to Cartesian  coordinates. The axial
 alignments of this transformation are described in
 [\_atom\_sites\_Cartn\_transform\_axes](#_atom_sites_Cartn_transform_axes). The 3 x 1 translation is
 defined in \_atom\_sites\_Cartn\_tran\_vector\_.
   x&#39;                   |11 12 13|      x                  | 1 |
 ( y&#39; ) Cartesian   =   |21 22 23|    ( y ) fractional  +  | 2 |
   z&#39;                   |31 32 33|      z                  | 3 |

### <a name="_atom_sites_Cartn_tran_matrix_31"></a>\_atom\_sites\_Cartn\_tran\_matrix\_31

Matrix elements used to transform fractional coordinates in
 the ATOM\_SITE category to Cartesian  coordinates. The axial
 alignments of this transformation are described in
 [\_atom\_sites\_Cartn\_transform\_axes](#_atom_sites_Cartn_transform_axes). The 3 x 1 translation is
 defined in \_atom\_sites\_Cartn\_tran\_vector\_.
   x&#39;                   |11 12 13|      x                  | 1 |
 ( y&#39; ) Cartesian   =   |21 22 23|    ( y ) fractional  +  | 2 |
   z&#39;                   |31 32 33|      z                  | 3 |

### <a name="_atom_sites_Cartn_tran_matrix_32"></a>\_atom\_sites\_Cartn\_tran\_matrix\_32

Matrix elements used to transform fractional coordinates in
 the ATOM\_SITE category to Cartesian  coordinates. The axial
 alignments of this transformation are described in
 [\_atom\_sites\_Cartn\_transform\_axes](#_atom_sites_Cartn_transform_axes). The 3 x 1 translation is
 defined in \_atom\_sites\_Cartn\_tran\_vector\_.
   x&#39;                   |11 12 13|      x                  | 1 |
 ( y&#39; ) Cartesian   =   |21 22 23|    ( y ) fractional  +  | 2 |
   z&#39;                   |31 32 33|      z                  | 3 |

### <a name="_atom_sites_Cartn_tran_matrix_33"></a>\_atom\_sites\_Cartn\_tran\_matrix\_33

Matrix elements used to transform fractional coordinates in
 the ATOM\_SITE category to Cartesian  coordinates. The axial
 alignments of this transformation are described in
 [\_atom\_sites\_Cartn\_transform\_axes](#_atom_sites_Cartn_transform_axes). The 3 x 1 translation is
 defined in \_atom\_sites\_Cartn\_tran\_vector\_.
   x&#39;                   |11 12 13|      x                  | 1 |
 ( y&#39; ) Cartesian   =   |21 22 23|    ( y ) fractional  +  | 2 |
   z&#39;                   |31 32 33|      z                  | 3 |

### <a name="_atom_sites_Cartn_tran_vector_1"></a>\_atom\_sites\_Cartn\_tran\_vector\_1

Elements of a 3 x 1 translation vector used in the
 transformation of fractional coordinates in the
 ATOM\_SITE category to Cartesian  coordinates. The axial
 alignments of this transformation are described in
 [\_atom\_sites\_Cartn\_transform\_axes](#_atom_sites_Cartn_transform_axes).
   x&#39;                   |11 12 13|      x                  | 1 |
 ( y&#39; ) Cartesian   =   |21 22 23|    ( y ) fractional  +  | 2 |
   z&#39;                   |31 32 33|      z                  | 3 |

### <a name="_atom_sites_Cartn_tran_vector_2"></a>\_atom\_sites\_Cartn\_tran\_vector\_2

Elements of a 3 x 1 translation vector used in the
 transformation of fractional coordinates in the
 ATOM\_SITE category to Cartesian  coordinates. The axial
 alignments of this transformation are described in
 [\_atom\_sites\_Cartn\_transform\_axes](#_atom_sites_Cartn_transform_axes).
   x&#39;                   |11 12 13|      x                  | 1 |
 ( y&#39; ) Cartesian   =   |21 22 23|    ( y ) fractional  +  | 2 |
   z&#39;                   |31 32 33|      z                  | 3 |

### <a name="_atom_sites_Cartn_tran_vector_3"></a>\_atom\_sites\_Cartn\_tran\_vector\_3

Elements of a 3 x 1 translation vector used in the
 transformation of fractional coordinates in the
 ATOM\_SITE category to Cartesian  coordinates. The axial
 alignments of this transformation are described in
 [\_atom\_sites\_Cartn\_transform\_axes](#_atom_sites_Cartn_transform_axes).
   x&#39;                   |11 12 13|      x                  | 1 |
 ( y&#39; ) Cartesian   =   |21 22 23|    ( y ) fractional  +  | 2 |
   z&#39;                   |31 32 33|      z                  | 3 |

### <a name="_atom_sites_Cartn_transform_axes"></a>\_atom\_sites\_Cartn\_transform\_axes

A description of the relative alignment of the crystal cell
 axes to the  Cartesian orthogonal axes as applied in the
 transformation matrix \_atom\_sites\_Cartn\_tran\_matrix\_.

### <a name="_atom_sites_fract_tran_matrix_11"></a>\_atom\_sites\_fract\_tran\_matrix\_11

Matrix elements used to transform Cartesian coordinates in
 the ATOM\_SITE category to fractional coordinates. The axial
 alignments of this transformation are described in
 [\_atom\_sites\_Cartn\_transform\_axes](#_atom_sites_Cartn_transform_axes). The 3 x 1 translation is
 defined in \_atom\_sites\_fract\_tran\_vector\_.
   x&#39;                   |11 12 13|      x                 | 1 |
 ( y&#39; ) fractional  =   |21 22 23|    ( y ) Cartesian  +  | 2 |
   z&#39;                   |31 32 33|      z                 | 3 |

### <a name="_atom_sites_fract_tran_matrix_12"></a>\_atom\_sites\_fract\_tran\_matrix\_12

Matrix elements used to transform Cartesian coordinates in
 the ATOM\_SITE category to fractional coordinates. The axial
 alignments of this transformation are described in
 [\_atom\_sites\_Cartn\_transform\_axes](#_atom_sites_Cartn_transform_axes). The 3 x 1 translation is
 defined in \_atom\_sites\_fract\_tran\_vector\_.
   x&#39;                   |11 12 13|      x                 | 1 |
 ( y&#39; ) fractional  =   |21 22 23|    ( y ) Cartesian  +  | 2 |
   z&#39;                   |31 32 33|      z                 | 3 |

### <a name="_atom_sites_fract_tran_matrix_13"></a>\_atom\_sites\_fract\_tran\_matrix\_13

Matrix elements used to transform Cartesian coordinates in
 the ATOM\_SITE category to fractional coordinates. The axial
 alignments of this transformation are described in
 [\_atom\_sites\_Cartn\_transform\_axes](#_atom_sites_Cartn_transform_axes). The 3 x 1 translation is
 defined in \_atom\_sites\_fract\_tran\_vector\_.
   x&#39;                   |11 12 13|      x                 | 1 |
 ( y&#39; ) fractional  =   |21 22 23|    ( y ) Cartesian  +  | 2 |
   z&#39;                   |31 32 33|      z                 | 3 |

### <a name="_atom_sites_fract_tran_matrix_21"></a>\_atom\_sites\_fract\_tran\_matrix\_21

Matrix elements used to transform Cartesian coordinates in
 the ATOM\_SITE category to fractional coordinates. The axial
 alignments of this transformation are described in
 [\_atom\_sites\_Cartn\_transform\_axes](#_atom_sites_Cartn_transform_axes). The 3 x 1 translation is
 defined in \_atom\_sites\_fract\_tran\_vector\_.
   x&#39;                   |11 12 13|      x                 | 1 |
 ( y&#39; ) fractional  =   |21 22 23|    ( y ) Cartesian  +  | 2 |
   z&#39;                   |31 32 33|      z                 | 3 |

### <a name="_atom_sites_fract_tran_matrix_22"></a>\_atom\_sites\_fract\_tran\_matrix\_22

Matrix elements used to transform Cartesian coordinates in
 the ATOM\_SITE category to fractional coordinates. The axial
 alignments of this transformation are described in
 [\_atom\_sites\_Cartn\_transform\_axes](#_atom_sites_Cartn_transform_axes). The 3 x 1 translation is
 defined in \_atom\_sites\_fract\_tran\_vector\_.
   x&#39;                   |11 12 13|      x                 | 1 |
 ( y&#39; ) fractional  =   |21 22 23|    ( y ) Cartesian  +  | 2 |
   z&#39;                   |31 32 33|      z                 | 3 |

### <a name="_atom_sites_fract_tran_matrix_23"></a>\_atom\_sites\_fract\_tran\_matrix\_23

Matrix elements used to transform Cartesian coordinates in
 the ATOM\_SITE category to fractional coordinates. The axial
 alignments of this transformation are described in
 [\_atom\_sites\_Cartn\_transform\_axes](#_atom_sites_Cartn_transform_axes). The 3 x 1 translation is
 defined in \_atom\_sites\_fract\_tran\_vector\_.
   x&#39;                   |11 12 13|      x                 | 1 |
 ( y&#39; ) fractional  =   |21 22 23|    ( y ) Cartesian  +  | 2 |
   z&#39;                   |31 32 33|      z                 | 3 |

### <a name="_atom_sites_fract_tran_matrix_31"></a>\_atom\_sites\_fract\_tran\_matrix\_31

Matrix elements used to transform Cartesian coordinates in
 the ATOM\_SITE category to fractional coordinates. The axial
 alignments of this transformation are described in
 [\_atom\_sites\_Cartn\_transform\_axes](#_atom_sites_Cartn_transform_axes). The 3 x 1 translation is
 defined in \_atom\_sites\_fract\_tran\_vector\_.
   x&#39;                   |11 12 13|      x                 | 1 |
 ( y&#39; ) fractional  =   |21 22 23|    ( y ) Cartesian  +  | 2 |
   z&#39;                   |31 32 33|      z                 | 3 |

### <a name="_atom_sites_fract_tran_matrix_32"></a>\_atom\_sites\_fract\_tran\_matrix\_32

Matrix elements used to transform Cartesian coordinates in
 the ATOM\_SITE category to fractional coordinates. The axial
 alignments of this transformation are described in
 [\_atom\_sites\_Cartn\_transform\_axes](#_atom_sites_Cartn_transform_axes). The 3 x 1 translation is
 defined in \_atom\_sites\_fract\_tran\_vector\_.
   x&#39;                   |11 12 13|      x                 | 1 |
 ( y&#39; ) fractional  =   |21 22 23|    ( y ) Cartesian  +  | 2 |
   z&#39;                   |31 32 33|      z                 | 3 |

### <a name="_atom_sites_fract_tran_matrix_33"></a>\_atom\_sites\_fract\_tran\_matrix\_33

Matrix elements used to transform Cartesian coordinates in
 the ATOM\_SITE category to fractional coordinates. The axial
 alignments of this transformation are described in
 [\_atom\_sites\_Cartn\_transform\_axes](#_atom_sites_Cartn_transform_axes). The 3 x 1 translation is
 defined in \_atom\_sites\_fract\_tran\_vector\_.
   x&#39;                   |11 12 13|      x                 | 1 |
 ( y&#39; ) fractional  =   |21 22 23|    ( y ) Cartesian  +  | 2 |
   z&#39;                   |31 32 33|      z                 | 3 |

### <a name="_atom_sites_fract_tran_vector_1"></a>\_atom\_sites\_fract\_tran\_vector\_1

Elements of a 3 x 1 translation vector used in the
 transformation of Cartesian coordinates in the
 ATOM\_SITE category to fractional  coordinates. The axial
 alignments of this transformation are described in
 [\_atom\_sites\_Cartn\_transform\_axes](#_atom_sites_Cartn_transform_axes).
   x&#39;                   |11 12 13|      x                 | 1 |
 ( y&#39; ) fractional  =   |21 22 23|    ( y ) Cartesian  +  | 2 |
   z&#39;                   |31 32 33|      z                 | 3 |

### <a name="_atom_sites_fract_tran_vector_2"></a>\_atom\_sites\_fract\_tran\_vector\_2

Elements of a 3 x 1 translation vector used in the
 transformation of Cartesian coordinates in the
 ATOM\_SITE category to fractional  coordinates. The axial
 alignments of this transformation are described in
 [\_atom\_sites\_Cartn\_transform\_axes](#_atom_sites_Cartn_transform_axes).
   x&#39;                   |11 12 13|      x                 | 1 |
 ( y&#39; ) fractional  =   |21 22 23|    ( y ) Cartesian  +  | 2 |
   z&#39;                   |31 32 33|      z                 | 3 |

### <a name="_atom_sites_fract_tran_vector_3"></a>\_atom\_sites\_fract\_tran\_vector\_3

Elements of a 3 x 1 translation vector used in the
 transformation of Cartesian coordinates in the
 ATOM\_SITE category to fractional  coordinates. The axial
 alignments of this transformation are described in
 [\_atom\_sites\_Cartn\_transform\_axes](#_atom_sites_Cartn_transform_axes).
   x&#39;                   |11 12 13|      x                 | 1 |
 ( y&#39; ) fractional  =   |21 22 23|    ( y ) Cartesian  +  | 2 |
   z&#39;                   |31 32 33|      z                 | 3 |

### <a name="_atom_sites_solution_primary"></a>\_atom\_sites\_solution\_primary

Codes which identify the methods used to locate the initial
 atom sites. The \*\_primary code identifies how the first
 atom sites were determined; the \*\_secondary code identifies
 how the remaining non-hydrogen sites were located; and the
 \*\_hydrogens code identifies how the hydrogen sites were located.

 Ref: Sheldrick, G. M., Hauptman, H. A., Weeks, C. M.,
      Miller, R. and Us&oacute;n, I. (2001). Ab initio phasing.
      In International Tables for Crystallography,
      Vol. F. Crystallography of biological macromolecules,
      edited by M. G. Rossmann and E. Arnold, ch. 16.1.
      Dordrecht: Kluwer Academic Publishers.

Values:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>difmap</td><td>difference Fourier map</td></tr>
  <tr><td>vecmap</td><td>real-space vector search</td></tr>
  <tr><td>heavy</td><td>heavy-atom method</td></tr>
  <tr><td>direct</td><td>structure-invariant direct methods</td></tr>
  <tr><td>geom</td><td>inferred from neighbouring sites</td></tr>
  <tr><td>disper</td><td>anomalous-dispersion techniques</td></tr>
  <tr><td>isomor</td><td>isomorphous structure methods</td></tr>
  <tr><td>notdet</td><td>coordinates were not determined</td></tr>
  <tr><td>dual</td><td>dual-space method (Sheldrick et al., 2001)</td></tr>
  <tr><td>other</td><td>a method not included elsewhere in this list</td></tr>
</table>
### <a name="_atom_sites_solution_secondary"></a>\_atom\_sites\_solution\_secondary

Codes which identify the methods used to locate the initial
 atom sites. The \*\_primary code identifies how the first
 atom sites were determined; the \*\_secondary code identifies
 how the remaining non-hydrogen sites were located; and the
 \*\_hydrogens code identifies how the hydrogen sites were located.

 Ref: Sheldrick, G. M., Hauptman, H. A., Weeks, C. M.,
      Miller, R. and Us&oacute;n, I. (2001). Ab initio phasing.
      In International Tables for Crystallography,
      Vol. F. Crystallography of biological macromolecules,
      edited by M. G. Rossmann and E. Arnold, ch. 16.1.
      Dordrecht: Kluwer Academic Publishers.

Values:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>difmap</td><td>difference Fourier map</td></tr>
  <tr><td>vecmap</td><td>real-space vector search</td></tr>
  <tr><td>heavy</td><td>heavy-atom method</td></tr>
  <tr><td>direct</td><td>structure-invariant direct methods</td></tr>
  <tr><td>geom</td><td>inferred from neighbouring sites</td></tr>
  <tr><td>disper</td><td>anomalous-dispersion techniques</td></tr>
  <tr><td>isomor</td><td>isomorphous structure methods</td></tr>
  <tr><td>notdet</td><td>coordinates were not determined</td></tr>
  <tr><td>dual</td><td>dual-space method (Sheldrick et al., 2001)</td></tr>
  <tr><td>other</td><td>a method not included elsewhere in this list</td></tr>
</table>
### <a name="_atom_sites_solution_hydrogens"></a>\_atom\_sites\_solution\_hydrogens

Codes which identify the methods used to locate the initial
 atom sites. The \*\_primary code identifies how the first
 atom sites were determined; the \*\_secondary code identifies
 how the remaining non-hydrogen sites were located; and the
 \*\_hydrogens code identifies how the hydrogen sites were located.

 Ref: Sheldrick, G. M., Hauptman, H. A., Weeks, C. M.,
      Miller, R. and Us&oacute;n, I. (2001). Ab initio phasing.
      In International Tables for Crystallography,
      Vol. F. Crystallography of biological macromolecules,
      edited by M. G. Rossmann and E. Arnold, ch. 16.1.
      Dordrecht: Kluwer Academic Publishers.

Values:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>difmap</td><td>difference Fourier map</td></tr>
  <tr><td>vecmap</td><td>real-space vector search</td></tr>
  <tr><td>heavy</td><td>heavy-atom method</td></tr>
  <tr><td>direct</td><td>structure-invariant direct methods</td></tr>
  <tr><td>geom</td><td>inferred from neighbouring sites</td></tr>
  <tr><td>disper</td><td>anomalous-dispersion techniques</td></tr>
  <tr><td>isomor</td><td>isomorphous structure methods</td></tr>
  <tr><td>notdet</td><td>coordinates were not determined</td></tr>
  <tr><td>dual</td><td>dual-space method (Sheldrick et al., 2001)</td></tr>
  <tr><td>other</td><td>a method not included elsewhere in this list</td></tr>
</table>
### <a name="_atom_sites_special_details"></a>\_atom\_sites\_special\_details

Additional information about the atomic coordinates not coded
 elsewhere in the CIF.

## <a name="ATOM_TYPE"></a>ATOM\_TYPE

Data items in the ATOM\_TYPE category record details about
 properties of the atoms that occupy the atom sites, such as the
 atomic scattering factors.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
_atom_type_symbol
_atom_type_oxidation_number
_atom_type_number_in_cell
_atom_type_scat_dispersion_real
_atom_type_scat_dispersion_imag
_atom_type_scat_source
  C 0 72  .017  .009  International_Tables_Vol_IV_Table_2.2B
  H 0 100  0     0    International_Tables_Vol_IV_Table_2.2B
  O 0 12  .047  .032  International_Tables_Vol_IV_Table_2.2B
  N 0 4   .029  .018  International_Tables_Vol_IV_Table_2.2B
</code></pre>
  </td><td>Example 1 - based on data set TOZ of Willis, Beckwith &amp; Tozer
            [Acta Cryst. (1991), C47, 2276-2277].
  </td></tr>
</table>
### <a name="_atom_type_analytical_mass_%"></a>\_atom\_type\_analytical\_mass\_%

Mass percentage of this atom type derived from chemical analysis.

### <a name="_atom_type_description"></a>\_atom\_type\_description

A description of the atom(s) designated by this atom type. In
 most cases, this will be the element name and oxidation state of
 a single atom  species. For disordered or nonstoichiometric
 structures it will describe a combination of atom species.

### <a name="_atom_type_number_in_cell"></a>\_atom\_type\_number\_in\_cell

Total number of atoms of this atom type in the unit cell.

### <a name="_atom_type_oxidation_number"></a>\_atom\_type\_oxidation\_number

Formal oxidation state of this atom type in the structure.

Default value: '0'

### <a name="_atom_type_radius_bond"></a>\_atom\_type\_radius\_bond

The effective intra- and intermolecular bonding radii in
 angstroms of this atom type.

Units: angstroms

### <a name="_atom_type_radius_contact"></a>\_atom\_type\_radius\_contact

The effective intra- and intermolecular bonding radii in
 angstroms of this atom type.

Units: angstroms

### <a name="_atom_type_scat_Cromer_Mann_a1"></a>\_atom\_type\_scat\_Cromer\_Mann\_a1

The Cromer-Mann scattering-factor coefficients used to calculate
 the scattering factors for this atom type.

 Ref: International Tables for X-ray Crystallography (1974). 
       Vol. IV, Table 2.2B
 or   International Tables for Crystallography (2004). Vol. C,
      Tables 6.1.1.4 and 6.1.1.5

### <a name="_atom_type_scat_Cromer_Mann_a2"></a>\_atom\_type\_scat\_Cromer\_Mann\_a2

The Cromer-Mann scattering-factor coefficients used to calculate
 the scattering factors for this atom type.

 Ref: International Tables for X-ray Crystallography (1974). 
       Vol. IV, Table 2.2B
 or   International Tables for Crystallography (2004). Vol. C,
      Tables 6.1.1.4 and 6.1.1.5

### <a name="_atom_type_scat_Cromer_Mann_a3"></a>\_atom\_type\_scat\_Cromer\_Mann\_a3

The Cromer-Mann scattering-factor coefficients used to calculate
 the scattering factors for this atom type.

 Ref: International Tables for X-ray Crystallography (1974). 
       Vol. IV, Table 2.2B
 or   International Tables for Crystallography (2004). Vol. C,
      Tables 6.1.1.4 and 6.1.1.5

### <a name="_atom_type_scat_Cromer_Mann_a4"></a>\_atom\_type\_scat\_Cromer\_Mann\_a4

The Cromer-Mann scattering-factor coefficients used to calculate
 the scattering factors for this atom type.

 Ref: International Tables for X-ray Crystallography (1974). 
       Vol. IV, Table 2.2B
 or   International Tables for Crystallography (2004). Vol. C,
      Tables 6.1.1.4 and 6.1.1.5

### <a name="_atom_type_scat_Cromer_Mann_b1"></a>\_atom\_type\_scat\_Cromer\_Mann\_b1

The Cromer-Mann scattering-factor coefficients used to calculate
 the scattering factors for this atom type.

 Ref: International Tables for X-ray Crystallography (1974). 
       Vol. IV, Table 2.2B
 or   International Tables for Crystallography (2004). Vol. C,
      Tables 6.1.1.4 and 6.1.1.5

### <a name="_atom_type_scat_Cromer_Mann_b2"></a>\_atom\_type\_scat\_Cromer\_Mann\_b2

The Cromer-Mann scattering-factor coefficients used to calculate
 the scattering factors for this atom type.

 Ref: International Tables for X-ray Crystallography (1974). 
       Vol. IV, Table 2.2B
 or   International Tables for Crystallography (2004). Vol. C,
      Tables 6.1.1.4 and 6.1.1.5

### <a name="_atom_type_scat_Cromer_Mann_b3"></a>\_atom\_type\_scat\_Cromer\_Mann\_b3

The Cromer-Mann scattering-factor coefficients used to calculate
 the scattering factors for this atom type.

 Ref: International Tables for X-ray Crystallography (1974). 
       Vol. IV, Table 2.2B
 or   International Tables for Crystallography (2004). Vol. C,
      Tables 6.1.1.4 and 6.1.1.5

### <a name="_atom_type_scat_Cromer_Mann_b4"></a>\_atom\_type\_scat\_Cromer\_Mann\_b4

The Cromer-Mann scattering-factor coefficients used to calculate
 the scattering factors for this atom type.

 Ref: International Tables for X-ray Crystallography (1974). 
       Vol. IV, Table 2.2B
 or   International Tables for Crystallography (2004). Vol. C,
      Tables 6.1.1.4 and 6.1.1.5

### <a name="_atom_type_scat_Cromer_Mann_c"></a>\_atom\_type\_scat\_Cromer\_Mann\_c

The Cromer-Mann scattering-factor coefficients used to calculate
 the scattering factors for this atom type.

 Ref: International Tables for X-ray Crystallography (1974). 
       Vol. IV, Table 2.2B
 or   International Tables for Crystallography (2004). Vol. C,
      Tables 6.1.1.4 and 6.1.1.5

### <a name="_atom_type_scat_dispersion_imag"></a>\_atom\_type\_scat\_dispersion\_imag

The imaginary and real components of the anomalous-dispersion
 scattering factor, f&#39;&#39; and f&#39;, in electrons for this atom type
 and the radiation given in [\_diffrn\_radiation\_wavelength](#_diffrn_radiation_wavelength).

Default value: '0.0'

### <a name="_atom_type_scat_dispersion_real"></a>\_atom\_type\_scat\_dispersion\_real

The imaginary and real components of the anomalous-dispersion
 scattering factor, f&#39;&#39; and f&#39;, in electrons for this atom type
 and the radiation given in [\_diffrn\_radiation\_wavelength](#_diffrn_radiation_wavelength).

Default value: '0.0'

### <a name="_atom_type_scat_dispersion_source"></a>\_atom\_type\_scat\_dispersion\_source

Reference to source of real and imaginary dispersion
 corrections for scattering factors used for this atom type.

### <a name="_atom_type_scat_length_neutron"></a>\_atom\_type\_scat\_length\_neutron

The bound coherent scattering length in femtometres for the
 atom type at the isotopic composition used for the diffraction
 experiment.

Units: femtometres

Default value: '0.0'

### <a name="_atom_type_scat_source"></a>\_atom\_type\_scat\_source

Reference to source of scattering factors or scattering lengths
 used for this atom type.

### <a name="_atom_type_scat_versus_stol_list"></a>\_atom\_type\_scat\_versus\_stol\_list

A table of scattering factors as a function of sin theta over
 lambda. This table should be well commented to indicate the
 items present. Regularly formatted lists are strongly
 recommended.

### <a name="_atom_type_symbol"></a>\_atom\_type\_symbol

The code used to identify the atom species (singular or plural)
 representing this atom type. Normally this code is the element
 symbol. The code may be composed of any character except an
 underscore with the additional proviso that digits designate an
 oxidation state and must be followed by a + or - character.

## <a name="AUDIT"></a>AUDIT

Data items in the AUDIT category record details about the
 creation and subsequent updating of the data block.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
_audit_block_code                  TOZ_1991-03-20

_audit_creation_date               1991-03-20
_audit_creation_method   from_xtal_archive_file_using_CIFIO
_audit_update_record
; 1991-04-09     text and data added by Tony Willis.
  1991-04-15     rec&#39;d by co-editor as manuscript HL0007.
  1991-04-17     adjustments based on first referee report.
  1991-04-18     adjustments based on second referee report.
;
</code></pre>
  </td><td>Example 1 - based on data set TOZ of Willis, Beckwith &amp; Tozer
            [Acta Cryst. (1991), C47, 2276-2277].
  </td></tr>
</table>
### <a name="_audit_block_code"></a>\_audit\_block\_code

A code intended to identify uniquely the current data block.

### <a name="_audit_creation_date"></a>\_audit\_creation\_date

The date that the data block was created. The date format
 is yyyy-mm-dd.

### <a name="_audit_creation_method"></a>\_audit\_creation\_method

A description of how data were entered into the data block.

### <a name="_audit_update_record"></a>\_audit\_update\_record

A record of any changes to the data block. The update format
 is a date (yyyy-mm-dd) followed by a description of the
 changes. The latest update entry is added to the bottom of
 this record.

## <a name="AUDIT_AUTHOR"></a>AUDIT\_AUTHOR

Data items in the AUDIT\_AUTHOR category record details about
 the author(s) of the data block.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
_audit_author_name
_audit_author_address
    &#39;Fitzgerald, Paula M. D.&#39;
;  Department of Biophysical Chemistry
   Merck Research Laboratories
   PO Box 2000, Ry80M203
   Rahway
   New Jersey 07065
   USA
;
    &#39;Van Middlesworth, J. F.&#39;
;  Department of Biophysical Chemistry
   Merck Research Laboratories
   PO Box 2000, Ry80M203
   Rahway
   New Jersey 07065
   USA
;
</code></pre>
  </td><td>Example 1 - based on PDB entry 5HVP and laboratory records for the
            structure corresponding to PDB entry 5HVP.
  </td></tr>
</table>
### <a name="_audit_author_address"></a>\_audit\_author\_address

The address of an author of this data block. If there are
 multiple authors, [\_audit\_author\_address](#_audit_author_address) is looped with
 [\_audit\_author\_name](#_audit_author_name).

### <a name="_audit_author_name"></a>\_audit\_author\_name

The name of an author of this data block. If there are multiple
 authors, [\_audit\_author\_name](#_audit_author_name) is looped with [\_audit\_author\_address](#_audit_author_address).
 The family name(s), followed by a comma and including any
 dynastic components, precedes the first name(s) or initial(s).

## <a name="AUDIT_CONFORM"></a>AUDIT\_CONFORM

Data items in the AUDIT\_CONFORM category describe the
 dictionary versions against which the data names appearing in
 the current data block are conformant.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
_audit_conform_dict_name         cif_core.dic
_audit_conform_dict_version      2.4
_audit_conform_dict_location
      ftp://ftp.iucr.org/pub/cif_core.2.4.dic
</code></pre>
  </td><td>Example 1 - any file conforming to the current CIF core dictionary.
  </td></tr>
</table>
### <a name="_audit_conform_dict_location"></a>\_audit\_conform\_dict\_location

A file name or uniform resource locator (URL) for the
 dictionary to which the current data block conforms.

### <a name="_audit_conform_dict_name"></a>\_audit\_conform\_dict\_name

The string identifying the highest-level dictionary defining
 data names used in this file.

### <a name="_audit_conform_dict_version"></a>\_audit\_conform\_dict\_version

The version number of the dictionary to which the
 current data block conforms.

## <a name="AUDIT_CONTACT_AUTHOR"></a>AUDIT\_CONTACT\_AUTHOR

Data items in the AUDIT\_CONTACT\_AUTHOR category record details
 about the name and address of the author to be contacted
 concerning the contents of this data block.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
_audit_contact_author_name
_audit_contact_author_address
_audit_contact_author_email
_audit_contact_author_fax
_audit_contact_author_phone
    &#39;Fitzgerald, Paula M. D.&#39;
;  Department of Biophysical Chemistry
   Merck Research Laboratories
   PO Box 2000, Ry80M203
   Rahway
   New Jersey 07065
   USA
;
    &#39;paula_fitzgerald@merck.com&#39;
    &#39;1(908)5945510&#39;
    &#39;1(908)5945510&#39;
</code></pre>
  </td><td>Example 1 - based on PDB entry 5HVP and laboratory records for the
            structure corresponding to PDB entry 5HVP.
  </td></tr>
</table>
### <a name="_audit_contact_author_address"></a>\_audit\_contact\_author\_address

The mailing address of the author of the data block to whom
 correspondence should be addressed.

### <a name="_audit_contact_author_email"></a>\_audit\_contact\_author\_email

The electronic mail address of the author of the data block
 to whom correspondence should be addressed, in a form
 recognizable to international networks. The format of e-mail 
 addresses is given in Section 3.4, Address Specification, of 
 Internet Message Format, RFC 2822, P. Resnick (Editor), 
 Network Standards Group, April 2001.

### <a name="_audit_contact_author_fax"></a>\_audit\_contact\_author\_fax

The facsimile telephone number of the author of the data
 block to whom correspondence should be addressed.

 The recommended style starts with the international dialing
 prefix, followed by the area code in parentheses, followed by the
 local number with no spaces.

### <a name="_audit_contact_author_name"></a>\_audit\_contact\_author\_name

The name of the author of the data block to whom correspondence
 should be addressed.

 The family name(s), followed by a comma and including any
 dynastic components, precedes the first name(s) or initial(s).

### <a name="_audit_contact_author_phone"></a>\_audit\_contact\_author\_phone

The telephone number of the author of the data block to whom
 correspondence should be addressed.

 The recommended style starts with the international dialing
 prefix, followed by the area code in parentheses, followed by the
 local number and any extension number prefixed by &#39;x&#39;,
 with no spaces.

## <a name="AUDIT_LINK"></a>AUDIT\_LINK

Data items in the AUDIT\_LINK category record details about the
 relationships between data blocks in the current CIF.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
_audit_link_block_code
_audit_link_block_description
   .         &#39;discursive text of paper with two structures&#39;
   morA_(1)  &#39;structure 1 of 2&#39;
   morA_(2)  &#39;structure 2 of 2&#39;
</code></pre>
  </td><td>Example 1 - multiple structure paper, as illustrated
            in A Guide to CIF for Authors (1995). IUCr: Chester.
  </td></tr>
  <tr><td>
<pre><code>
loop_
_audit_link_block_code
_audit_link_block_description
  .       &#39;publication details&#39;
  KSE_COM &#39;experimental data common to ref./mod. structures&#39;
  KSE_REF &#39;reference structure&#39;
  KSE_MOD &#39;modulated structure&#39;
</code></pre>
  </td><td>Example 2 - example file for the one-dimensional incommensurately
            modulated structure of K~2~SeO~4~.
  </td></tr>
</table>
### <a name="_audit_link_block_code"></a>\_audit\_link\_block\_code

The value of [\_audit\_block\_code](#_audit_block_code) associated with a data block
 in the current file related to the current data block. The
 special value &#39;.&#39; may be used to refer to the current data
 block for completeness.

### <a name="_audit_link_block_description"></a>\_audit\_link\_block\_description

A textual description of the relationship of the referenced
 data block to the current one.

## <a name="CELL"></a>CELL

Data items in the CELL category record details about the
 crystallographic cell parameters and their measurement.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
_cell_length_a                     5.959(1)
_cell_length_b                     14.956(1)
_cell_length_c                     19.737(3)
_cell_angle_alpha                  90
_cell_angle_beta                   90
_cell_angle_gamma                  90
_cell_volume                       1759.0(3)

_cell_measurement_temperature      293
_cell_measurement_reflns_used      25
_cell_measurement_theta_min        25
_cell_measurement_theta_max        31
</code></pre>
  </td><td>Example 1 - based on data set TOZ of Willis, Beckwith &amp; Tozer
            [Acta Cryst. (1991), C47, 2276-2277].
  </td></tr>
</table>
### <a name="_cell_angle_alpha"></a>\_cell\_angle\_alpha

Unit-cell angles of the reported structure in degrees.
 The values of [\_refln\_index\_h](#_refln_index_h), \*\_k, \*\_l must correspond to the
 cell defined by these values and [\_cell\_length\_a](#_cell_length_a), \*\_b and \*\_c.
 The values of [\_diffrn\_refln\_index\_h](#_diffrn_refln_index_h), \*\_k, \*\_l may not correspond
 to these values if a cell transformation took place following
 the measurement of the diffraction intensities. See also
 \_diffrn\_reflns\_transf\_matrix\_.

Units: degrees

Default value: '90.0'

### <a name="_cell_angle_beta"></a>\_cell\_angle\_beta

Unit-cell angles of the reported structure in degrees.
 The values of [\_refln\_index\_h](#_refln_index_h), \*\_k, \*\_l must correspond to the
 cell defined by these values and [\_cell\_length\_a](#_cell_length_a), \*\_b and \*\_c.
 The values of [\_diffrn\_refln\_index\_h](#_diffrn_refln_index_h), \*\_k, \*\_l may not correspond
 to these values if a cell transformation took place following
 the measurement of the diffraction intensities. See also
 \_diffrn\_reflns\_transf\_matrix\_.

Units: degrees

Default value: '90.0'

### <a name="_cell_angle_gamma"></a>\_cell\_angle\_gamma

Unit-cell angles of the reported structure in degrees.
 The values of [\_refln\_index\_h](#_refln_index_h), \*\_k, \*\_l must correspond to the
 cell defined by these values and [\_cell\_length\_a](#_cell_length_a), \*\_b and \*\_c.
 The values of [\_diffrn\_refln\_index\_h](#_diffrn_refln_index_h), \*\_k, \*\_l may not correspond
 to these values if a cell transformation took place following
 the measurement of the diffraction intensities. See also
 \_diffrn\_reflns\_transf\_matrix\_.

Units: degrees

Default value: '90.0'

### <a name="_cell_formula_units_Z"></a>\_cell\_formula\_units\_Z

The number of the formula units in the unit cell as specified
 by [\_chemical\_formula\_structural](#_chemical_formula_structural), [\_chemical\_formula\_moiety](#_chemical_formula_moiety) or
 [\_chemical\_formula\_sum](#_chemical_formula_sum).

### <a name="_cell_length_a"></a>\_cell\_length\_a

Unit-cell lengths in angstroms corresponding to the structure
 reported. The values of [\_refln\_index\_h](#_refln_index_h), \*\_k, \*\_l must
 correspond to the cell defined by these values and \_cell\_angle\_
 values. The values of [\_diffrn\_refln\_index\_h](#_diffrn_refln_index_h), \*\_k, \*\_l may not
 correspond to these values if a cell transformation took place
 following the measurement of the diffraction intensities. See
 also \_diffrn\_reflns\_transf\_matrix\_.

Units: angstroms

### <a name="_cell_length_b"></a>\_cell\_length\_b

Unit-cell lengths in angstroms corresponding to the structure
 reported. The values of [\_refln\_index\_h](#_refln_index_h), \*\_k, \*\_l must
 correspond to the cell defined by these values and \_cell\_angle\_
 values. The values of [\_diffrn\_refln\_index\_h](#_diffrn_refln_index_h), \*\_k, \*\_l may not
 correspond to these values if a cell transformation took place
 following the measurement of the diffraction intensities. See
 also \_diffrn\_reflns\_transf\_matrix\_.

Units: angstroms

### <a name="_cell_length_c"></a>\_cell\_length\_c

Unit-cell lengths in angstroms corresponding to the structure
 reported. The values of [\_refln\_index\_h](#_refln_index_h), \*\_k, \*\_l must
 correspond to the cell defined by these values and \_cell\_angle\_
 values. The values of [\_diffrn\_refln\_index\_h](#_diffrn_refln_index_h), \*\_k, \*\_l may not
 correspond to these values if a cell transformation took place
 following the measurement of the diffraction intensities. See
 also \_diffrn\_reflns\_transf\_matrix\_.

Units: angstroms

### <a name="_cell_measurement_pressure"></a>\_cell\_measurement\_pressure

The pressure in kilopascals at which the unit-cell parameters
 were measured (not the pressure at which the sample was
 synthesized).

Units: kilopascals

### <a name="_cell_measurement_radiation"></a>\_cell\_measurement\_radiation

Description of the radiation used to measure the unit-cell data.
 See also  [\_cell\_measurement\_wavelength](#_cell_measurement_wavelength).

### <a name="_cell_measurement_reflns_used"></a>\_cell\_measurement\_reflns\_used

The total number of reflections used to determine the unit cell.
 These reflections may be specified as [\_cell\_measurement\_refln](#_cell_measurement_refln)\_
 data items.

### <a name="_cell_measurement_temperature"></a>\_cell\_measurement\_temperature

The temperature in kelvins at which the unit-cell parameters
 were measured (not the temperature of synthesis).

Units: kelvin

### <a name="_cell_measurement_theta_max"></a>\_cell\_measurement\_theta\_max

The maximum and minimum theta angles of reflections
 used to measure the unit cell in degrees.

Units: degrees

### <a name="_cell_measurement_theta_min"></a>\_cell\_measurement\_theta\_min

The maximum and minimum theta angles of reflections
 used to measure the unit cell in degrees.

Units: degrees

### <a name="_cell_measurement_wavelength"></a>\_cell\_measurement\_wavelength

The wavelength in angstroms of the radiation used to measure
 the unit cell. If this is not specified, the wavelength is
 assumed to be the same as that given in
 [\_diffrn\_radiation\_wavelength](#_diffrn_radiation_wavelength).

Units: angstroms

### <a name="_cell_reciprocal_angle_alpha"></a>\_cell\_reciprocal\_angle\_alpha

The angles defining the reciprocal cell in degrees. These
 are related to those in the real cell by:

 cos(recip-alpha)
     = [cos(beta)\*cos(gamma) - cos(alpha)]/[sin(beta)\*sin(gamma)]

 cos(recip-beta)
     = [cos(gamma)\*cos(alpha) - cos(beta)]/[sin(gamma)\*sin(alpha)]

 cos(recip-gamma)
     = [cos(alpha)\*cos(beta) - cos(gamma)]/[sin(alpha)\*sin(beta)]

 Ref: Buerger, M. J. (1942). X-ray Crystallography, p. 360.
         New York: John Wiley &amp; Sons Inc.

Units: degrees

Default value: '90.0'

### <a name="_cell_reciprocal_angle_beta"></a>\_cell\_reciprocal\_angle\_beta

The angles defining the reciprocal cell in degrees. These
 are related to those in the real cell by:

 cos(recip-alpha)
     = [cos(beta)\*cos(gamma) - cos(alpha)]/[sin(beta)\*sin(gamma)]

 cos(recip-beta)
     = [cos(gamma)\*cos(alpha) - cos(beta)]/[sin(gamma)\*sin(alpha)]

 cos(recip-gamma)
     = [cos(alpha)\*cos(beta) - cos(gamma)]/[sin(alpha)\*sin(beta)]

 Ref: Buerger, M. J. (1942). X-ray Crystallography, p. 360.
         New York: John Wiley &amp; Sons Inc.

Units: degrees

Default value: '90.0'

### <a name="_cell_reciprocal_angle_gamma"></a>\_cell\_reciprocal\_angle\_gamma

The angles defining the reciprocal cell in degrees. These
 are related to those in the real cell by:

 cos(recip-alpha)
     = [cos(beta)\*cos(gamma) - cos(alpha)]/[sin(beta)\*sin(gamma)]

 cos(recip-beta)
     = [cos(gamma)\*cos(alpha) - cos(beta)]/[sin(gamma)\*sin(alpha)]

 cos(recip-gamma)
     = [cos(alpha)\*cos(beta) - cos(gamma)]/[sin(alpha)\*sin(beta)]

 Ref: Buerger, M. J. (1942). X-ray Crystallography, p. 360.
         New York: John Wiley &amp; Sons Inc.

Units: degrees

Default value: '90.0'

### <a name="_cell_reciprocal_length_a"></a>\_cell\_reciprocal\_length\_a

The reciprocal-cell lengths in inverse angstroms.  These are
 related to the real cell by:

 recip-a = b\*c\*sin(alpha)/V

 recip-b = c\*a\*sin(beta)/V

 recip-c = a\*b\*sin(gamma)/V

 where V is the cell volume.

 Ref: Buerger, M. J. (1942). X-ray Crystallography, p. 360.
         New York: John Wiley &amp; Sons Inc.

Units: reciprocal\_angstroms

### <a name="_cell_reciprocal_length_b"></a>\_cell\_reciprocal\_length\_b

The reciprocal-cell lengths in inverse angstroms.  These are
 related to the real cell by:

 recip-a = b\*c\*sin(alpha)/V

 recip-b = c\*a\*sin(beta)/V

 recip-c = a\*b\*sin(gamma)/V

 where V is the cell volume.

 Ref: Buerger, M. J. (1942). X-ray Crystallography, p. 360.
         New York: John Wiley &amp; Sons Inc.

Units: reciprocal\_angstroms

### <a name="_cell_reciprocal_length_c"></a>\_cell\_reciprocal\_length\_c

The reciprocal-cell lengths in inverse angstroms.  These are
 related to the real cell by:

 recip-a = b\*c\*sin(alpha)/V

 recip-b = c\*a\*sin(beta)/V

 recip-c = a\*b\*sin(gamma)/V

 where V is the cell volume.

 Ref: Buerger, M. J. (1942). X-ray Crystallography, p. 360.
         New York: John Wiley &amp; Sons Inc.

Units: reciprocal\_angstroms

### <a name="_cell_special_details"></a>\_cell\_special\_details

A description of special aspects of the cell choice, noting
 possible alternative settings.

### <a name="_cell_volume"></a>\_cell\_volume

Cell volume V in angstroms cubed.

 V = a b c [1 - cos^2^(alpha) - cos^2^(beta) - cos^2^(gamma)
             + 2 cos(alpha) cos(beta) cos(gamma) ] ^1/2^

 a     = [\_cell\_length\_a](#_cell_length_a)
 b     = [\_cell\_length\_b](#_cell_length_b)
 c     = [\_cell\_length\_c](#_cell_length_c)
 alpha = [\_cell\_angle\_alpha](#_cell_angle_alpha)
 beta  = [\_cell\_angle\_beta](#_cell_angle_beta)
 gamma = [\_cell\_angle\_gamma](#_cell_angle_gamma)

Units: cubic\_angstroms

## <a name="CELL_MEASUREMENT_REFLN"></a>CELL\_MEASUREMENT\_REFLN

Data items in the CELL\_MEASUREMENT\_REFLN category record
 details about the reflections used in the determination of the
 crystallographic cell parameters.

 The [\_cell\_measurement\_refln](#_cell_measurement_refln)\_ data items would in general be used
 only for diffractometer measurements.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
 _cell_measurement_refln_index_h
 _cell_measurement_refln_index_k
 _cell_measurement_refln_index_l
 _cell_measurement_refln_theta
   -2    4    1          8.67
    0    3    2          9.45
    3    0    2          9.46
   -3    4    1          8.93
   -2    1   -2          7.53
   10    0    0         23.77
    0   10    0         23.78
   -5    4    1         11.14
  # - - - - data truncated for brevity - - - -
</code></pre>
  </td><td>Example 1 - extracted from the CAD-4 listing for Rb~2~S~2~O~6~ at room
            temperature (unpublished).
  </td></tr>
</table>
### <a name="_cell_measurement_refln_index_h"></a>\_cell\_measurement\_refln\_index\_h

Miller indices of a reflection used for measurement of
 the unit cell.

### <a name="_cell_measurement_refln_index_k"></a>\_cell\_measurement\_refln\_index\_k

Miller indices of a reflection used for measurement of
 the unit cell.

### <a name="_cell_measurement_refln_index_l"></a>\_cell\_measurement\_refln\_index\_l

Miller indices of a reflection used for measurement of
 the unit cell.

### <a name="_cell_measurement_refln_theta"></a>\_cell\_measurement\_refln\_theta

Theta angle in degrees for the reflection used for
 measurement of the unit cell with the indices
 \_cell\_measurement\_refln\_index\_.

Units: degrees

## <a name="CHEMICAL"></a>CHEMICAL

Data items in the CHEMICAL category record details about the
 composition and chemical properties of the compound. The
 formula data items must agree with those that specify the
 density, unit-cell and Z values.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
_chemical_name_systematic
  trans-bis(tricyclohexylphosphine)tetracarbonylmolybdenum(0)
</code></pre>
  </td><td>Example 1 - based on data set 9597gaus of Alyea, Ferguson &amp; Kannan
            [Acta Cryst. (1996), C52, 765-767].
  </td></tr>
</table>
### <a name="_chemical_absolute_configuration"></a>\_chemical\_absolute\_configuration

Necessary conditions for the assignment of
 [\_chemical\_absolute\_configuration](#_chemical_absolute_configuration) are given by H. D. Flack and
 G. Bernardinelli (1999, 2000).

 Ref: Flack, H. D. &amp; Bernardinelli, G. (1999). Acta Cryst. A55,
         908-915. ([http://www.iucr.org/paper?sh0129](http://www.iucr.org/paper?sh0129))
      Flack, H. D. &amp; Bernardinelli, G. (2000). J. Appl. Cryst.
         33, 1143-1148. ([http://www.iucr.org/paper?ks0021](http://www.iucr.org/paper?ks0021))

Values:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>rm</td><td>Absolute configuration established by
 the structure determination of a
 compound containing a chiral reference
 molecule of known absolute
 configuration.</td></tr>
  <tr><td>ad</td><td>Absolute configuration established by
 anomalous-dispersion effects in
 diffraction measurements on the
 crystal.</td></tr>
  <tr><td>rmad</td><td>Absolute configuration established by
 the structure determination of a
 compound containing a chiral reference
 molecule of known absolute
 configuration and confirmed by
 anomalous-dispersion effects in
 diffraction measurements on the
 crystal.</td></tr>
  <tr><td>syn</td><td>Absolute configuration has not been
 established by anomalous-dispersion
 effects in diffraction measurements on
 the crystal. The enantiomer has been
 assigned by reference to an unchanging
 chiral centre in the synthetic
 procedure.</td></tr>
  <tr><td>unk</td><td>Absolute configuration is unknown,
 there being no firm chemical evidence
 for its assignment to hand and it
 having not been established by
 anomalous-dispersion effects in
 diffraction measurements on the
 crystal. An arbitrary choice of
 enantiomer has been made.</td></tr>
  <tr><td>.</td><td>Inapplicable.</td></tr>
</table>
### <a name="_chemical_compound_source"></a>\_chemical\_compound\_source

Description of the source of the compound under study, or of the
 parent  molecule if a simple derivative is studied. This includes
 the place of  discovery for minerals or the actual source of a
 natural product.

### <a name="_chemical_enantioexcess_bulk"></a>\_chemical\_enantioexcess\_bulk

The enantioexcess of the bulk material from which the 
 crystals were grown. A value of 0.0 indicates the
 racemate. A value of 1.0 indicates that the compound
 is enantiomerically pure.

 Enantioexcess is defined in the IUPAC Recommendations
 (Moss et al., 1996). The composition of the crystal
 and bulk must be the same.

 Ref: Moss G. P. et al. (1996). Basic Terminology of
      Stereochemistry. Pure Appl. Chem., 68, 2193-2222.
      [http://www.chem.qmul.ac.uk/iupac/stereo/index.html](http://www.chem.qmul.ac.uk/iupac/stereo/index.html) 

Units: dimensionless

### <a name="_chemical_enantioexcess_bulk_technique"></a>\_chemical\_enantioexcess\_bulk\_technique

The experimental technique used to determine the
 enantioexcess of the bulk compound.

Values:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>OA</td><td>Enantioexcess determined by
 measurement of the specific rotation
 of the optical activity of the bulk
 compound in solution.</td></tr>
  <tr><td>CD</td><td>Enantioexcess determined by
 measurement of the visible/near UV
 circular dichroism spectrum of the
 bulk compound in solution.</td></tr>
  <tr><td>EC</td><td>Enantioexcess determined by
 enantioselective chromatography of
 the bulk compound in solution.</td></tr>
  <tr><td>other</td><td>Enantioexcess determined by 
 a technique not included elsewhere
 in this list.</td></tr>
</table>
### <a name="_chemical_enantioexcess_crystal"></a>\_chemical\_enantioexcess\_crystal

The enantioexcess of the crystal used for the diffraction
 study. A value of 0.0 indicates the racemate. A value of
 1.0 indicates that the crystal is enantiomerically pure.

 Enantioexcess is defined in the IUPAC Recommendations
 (Moss et al., 1996).

 Ref: Moss G. P. et al. (1996). Basic Terminology of
      Stereochemistry. Pure Appl. Chem., 68, 2193-2222.
      [http://www.chem.qmul.ac.uk/iupac/stereo/index.html](http://www.chem.qmul.ac.uk/iupac/stereo/index.html) 

Units: dimensionless

### <a name="_chemical_enantioexcess_crystal_technique"></a>\_chemical\_enantioexcess\_crystal\_technique

The experimental technique used to determine the
 enantioexcess of the crystal.

Values:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>CD</td><td>Enantioexcess determined by
 measurement of the visible/near UV
 circular dichroism spectrum of the
 crystal taken into solution.</td></tr>
  <tr><td>EC</td><td>Enantioexcess determined by
 enantioselective chromatography of
 the crystal taken into solution.</td></tr>
  <tr><td>other</td><td>Enantioexcess determined by 
 a technique not included elsewhere
 in this list.</td></tr>
</table>
### <a name="_chemical_melting_point"></a>\_chemical\_melting\_point

The temperature in kelvins at which the crystalline solid changes
 to a liquid.

Units: kelvin

### <a name="_chemical_melting_point_gt"></a>\_chemical\_melting\_point\_gt

A temperature in kelvins below which (\*\_lt) or above
 which (\*\_gt) the melting point (the temperature at which the
 crystalline solid changes to a liquid) lies. These items allow a
 range of temperatures to be given.

 [\_chemical\_melting\_point](#_chemical_melting_point) should always be used in preference
 to these items whenever possible.

Units: kelvin

### <a name="_chemical_melting_point_lt"></a>\_chemical\_melting\_point\_lt

A temperature in kelvins below which (\*\_lt) or above
 which (\*\_gt) the melting point (the temperature at which the
 crystalline solid changes to a liquid) lies. These items allow a
 range of temperatures to be given.

 [\_chemical\_melting\_point](#_chemical_melting_point) should always be used in preference
 to these items whenever possible.

Units: kelvin

### <a name="_chemical_name_common"></a>\_chemical\_name\_common

Trivial name by which the compound is commonly known.

### <a name="_chemical_name_mineral"></a>\_chemical\_name\_mineral

Mineral name accepted by the International Mineralogical
 Association. Use only for natural minerals. See also
 [\_chemical\_compound\_source](#_chemical_compound_source).

### <a name="_chemical_name_structure_type"></a>\_chemical\_name\_structure\_type

Commonly used structure-type name. Usually only applied to
 minerals or inorganic compounds.

### <a name="_chemical_name_systematic"></a>\_chemical\_name\_systematic

IUPAC or Chemical Abstracts full name of the compound.

### <a name="_chemical_optical_rotation"></a>\_chemical\_optical\_rotation

The optical rotation in solution of the compound is
 specified in the following format:
      &#39;[&alpha;]^TEMP^~WAVE~ = SORT (c = CONC, SOLV)&#39;
 where:
   TEMP is the temperature of the measurement in degrees
        Celsius,
   WAVE is an indication of the wavelength of the light
        used for the measurement,
   CONC is the concentration of the solution given as the
        mass of the substance in g per 100 ml of solution,
   SORT is the signed value (preceded by a + or a - sign)
        of 100.&alpha;/(l.c), where &alpha; is the signed optical
        rotation in degrees measured in a cell of length l in
        dm and c is the value of CONC as defined above, and
   SOLV is the chemical formula of the solvent.

### <a name="_chemical_properties_biological"></a>\_chemical\_properties\_biological

A free-text description of the biological properties of the
 material.

### <a name="_chemical_properties_physical"></a>\_chemical\_properties\_physical

A free-text description of the physical properties of the
 material.

### <a name="_chemical_temperature_decomposition"></a>\_chemical\_temperature\_decomposition

The temperature in kelvins at which the solid decomposes.

Units: kelvin

### <a name="_chemical_temperature_decomposition_gt"></a>\_chemical\_temperature\_decomposition\_gt

A temperature in kelvins below which (\*\_lt) or above which
 (\*\_gt) the solid is known to decompose. These items allow
 a range of temperatures to be given.

 [\_chemical\_temperature\_decomposition](#_chemical_temperature_decomposition) should always be used in
 preference to these items whenever possible.

Units: kelvin

### <a name="_chemical_temperature_decomposition_lt"></a>\_chemical\_temperature\_decomposition\_lt

A temperature in kelvins below which (\*\_lt) or above which
 (\*\_gt) the solid is known to decompose. These items allow
 a range of temperatures to be given.

 [\_chemical\_temperature\_decomposition](#_chemical_temperature_decomposition) should always be used in
 preference to these items whenever possible.

Units: kelvin

### <a name="_chemical_temperature_sublimation"></a>\_chemical\_temperature\_sublimation

The temperature in kelvins at which the solid sublimes.

Units: kelvin

### <a name="_chemical_temperature_sublimation_gt"></a>\_chemical\_temperature\_sublimation\_gt

A temperature in kelvins below which (\*\_lt) or above which
 (\*\_gt) the solid is known to sublime. These items allow a
 range of temperatures to be given.

 [\_chemical\_temperature\_sublimation](#_chemical_temperature_sublimation) should always be used in
 preference to these items whenever possible.

Units: kelvin

### <a name="_chemical_temperature_sublimation_lt"></a>\_chemical\_temperature\_sublimation\_lt

A temperature in kelvins below which (\*\_lt) or above which
 (\*\_gt) the solid is known to sublime. These items allow a
 range of temperatures to be given.

 [\_chemical\_temperature\_sublimation](#_chemical_temperature_sublimation) should always be used in
 preference to these items whenever possible.

Units: kelvin

## <a name="CHEMICAL_CONN_ATOM"></a>CHEMICAL\_CONN\_ATOM

Data items in the [\_chemical\_conn\_atom](#_chemical_conn_atom)\_ and [\_chemical\_conn\_bond](#_chemical_conn_bond)\_
 categories record details about the two-dimensional (2D)
 chemical structure of the molecular species. They allow a 2D
 chemical diagram to be reconstructed for use in a publication or
 in a database search for structural and substructural
 relationships.

 The [\_chemical\_conn\_atom](#_chemical_conn_atom)\_ data items provide information about
 the chemical properties of the atoms in the structure. In cases
 where crystallographic and molecular symmetry elements coincide,
 they must also contain symmetry-generated atoms, so that the
 [\_chemical\_conn\_atom](#_chemical_conn_atom)\_ and [\_chemical\_conn\_bond](#_chemical_conn_bond)\_ data items will
 always describe a complete chemical entity.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
_chemical_conn_atom_number
_chemical_conn_atom_type_symbol
_chemical_conn_atom_display_x
_chemical_conn_atom_display_y
_chemical_conn_atom_NCA
_chemical_conn_atom_NH
    1   S    .39  .81   1   0
    2   S    .39  .96   2   0
    3   N    .14  .88   3   0
    4   C    .33  .88   3   0
    5   C    .11  .96   2   2
    6   C    .03  .96   2   2
    7   C    .03  .80   2   2
    8   C    .11  .80   2   2
    9   S    .54  .81   1   0
    10  S    .54  .96   2   0
    11  N    .80  .88   3   0
    12  C    .60  .88   3   0
    13  C    .84  .96   2   2
    14  C    .91  .96   2   2
    15  C    .91  .80   2   2
    16  C    .84  .80   2   2
</code></pre>
  </td><td>Example 1 - based on data set DPTD of Yamin, Suwandi, Fun, Sivakumar &amp;
            bin Shawkataly [Acta Cryst. (1996), C52, 951-953].
  </td></tr>
</table>
### <a name="_chemical_conn_atom_charge"></a>\_chemical\_conn\_atom\_charge

The net integer charge assigned to this atom. This is the
formal charge assignment normally found in chemical diagrams.

Default value: '0'

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
1
  </td><td>for an ammonium nitrogen
  </td></tr>
  <tr><td>
-1
  </td><td>for a chloride ion
  </td></tr>
</table>
### <a name="_chemical_conn_atom_display_x"></a>\_chemical\_conn\_atom\_display\_x

The 2D Cartesian coordinates (x,y) of the position of this atom
 in a recognizable chemical diagram. The coordinate origin is at
 the lower left corner, the x axis is horizontal and the y axis is
 vertical. The coordinates must lie in the range 0.0 to 1.0. These
 coordinates can be obtained from projections of a suitable
 uncluttered view of the molecular structure.

### <a name="_chemical_conn_atom_display_y"></a>\_chemical\_conn\_atom\_display\_y

The 2D Cartesian coordinates (x,y) of the position of this atom
 in a recognizable chemical diagram. The coordinate origin is at
 the lower left corner, the x axis is horizontal and the y axis is
 vertical. The coordinates must lie in the range 0.0 to 1.0. These
 coordinates can be obtained from projections of a suitable
 uncluttered view of the molecular structure.

### <a name="_chemical_conn_atom_NCA"></a>\_chemical\_conn\_atom\_NCA

The number of connected atoms excluding terminal hydrogen atoms.

### <a name="_chemical_conn_atom_NH"></a>\_chemical\_conn\_atom\_NH

The total number of hydrogen atoms attached to this atom,
 regardless of whether they are included in the refinement or
 the [\_atom\_site](#_atom_site)\_ list. This number will be the same as
 [\_atom\_site\_attached\_hydrogens](#_atom_site_attached_hydrogens) only if none of the hydrogen
 atoms appear in the [\_atom\_site](#_atom_site)\_ list.

### <a name="_chemical_conn_atom_number"></a>\_chemical\_conn\_atom\_number

The chemical sequence number to be associated with this atom.

### <a name="_chemical_conn_atom_type_symbol"></a>\_chemical\_conn\_atom\_type\_symbol

A code identifying the atom type. This code must match an
 [\_atom\_type\_symbol](#_atom_type_symbol) code in the [\_atom\_type](#_atom_type)\_ list or be a
 recognizable element symbol.

## <a name="CHEMICAL_CONN_BOND"></a>CHEMICAL\_CONN\_BOND

Data items in the [\_chemical\_conn\_atom](#_chemical_conn_atom)\_ and [\_chemical\_conn\_bond](#_chemical_conn_bond)\_
 categories record details about the two-dimensional (2D)
 chemical structure of the molecular species. They allow a 2D
 chemical diagram to be reconstructed for use in a publication
 or in a database search for structural and substructural
 relationships.

 The [\_chemical\_conn\_bond](#_chemical_conn_bond)\_ data items specify the connections
 between the atoms in the [\_chemical\_conn\_atom](#_chemical_conn_atom)\_ list and the nature
 of the chemical bond between these atoms.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
_chemical_conn_bond_atom_1
_chemical_conn_bond_atom_2
_chemical_conn_bond_type
   4     1     doub     4     3     sing
   4     2     sing     5     3     sing
   6     5     sing     7     6     sing
   8     7     sing     8     3     sing
   10    2     sing     12    9     doub
   12    11    sing     12    10    sing
   13    11    sing     14    13    sing
   15    14    sing     16    15    sing
   16    11    sing     17    5     sing
   18    5     sing     19    6     sing
   20    6     sing     21    7     sing
   22    7     sing     23    8     sing
   24    8     sing     25    13    sing
   26    13    sing     27    14    sing
   28    14    sing     29    15    sing
   30    15    sing     31    16    sing
   32    16    sing
</code></pre>
  </td><td>Example 1 - based on data set DPTD of Yamin, Suwandi, Fun, Sivakumar &amp;
            bin Shawkataly [Acta Cryst. (1996), C52, 951-953].
  </td></tr>
</table>
### <a name="_chemical_conn_bond_atom_1"></a>\_chemical\_conn\_bond\_atom\_1

Atom numbers which must match with chemical sequence numbers
 specified as [\_chemical\_conn\_atom\_number](#_chemical_conn_atom_number) values. These link the
 bond connection to the chemical numbering and atom sites.

### <a name="_chemical_conn_bond_atom_2"></a>\_chemical\_conn\_bond\_atom\_2

Atom numbers which must match with chemical sequence numbers
 specified as [\_chemical\_conn\_atom\_number](#_chemical_conn_atom_number) values. These link the
 bond connection to the chemical numbering and atom sites.

### <a name="_chemical_conn_bond_type"></a>\_chemical\_conn\_bond\_type

The chemical bond type associated with the connection between
 the two sites \_chemical\_conn\_bond\_atom\_1 and \*\_2.

Values:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>sing</td><td>single bond</td></tr>
  <tr><td>doub</td><td>double bond</td></tr>
  <tr><td>trip</td><td>triple bond</td></tr>
  <tr><td>quad</td><td>quadruple bond</td></tr>
  <tr><td>arom</td><td>aromatic bond</td></tr>
  <tr><td>poly</td><td>polymeric bond</td></tr>
  <tr><td>delo</td><td>delocalized double bond</td></tr>
  <tr><td>pi</td><td>pi bond</td></tr>
</table>
Default value: 'sing'

## <a name="CHEMICAL_FORMULA"></a>CHEMICAL\_FORMULA

[\_chemical\_formula](#_chemical_formula)\_ items specify the composition and chemical
properties of the compound. The formula data items must agree
with those that specify the density, unit-cell and Z values.

The following rules apply to the construction of the data items
[\_chemical\_formula\_analytical](#_chemical_formula_analytical), \*\_structural and \*\_sum. For the
data item \*\_moiety, the formula construction is broken up into
residues or moieties, i.e. groups of atoms that form a molecular
unit or molecular ion. The  rules given below apply within each
moiety but different requirements apply to the way that moieties
are connected (see [\_chemical\_formula\_moiety](#_chemical_formula_moiety)).

(1) Only recognized element symbols may be used.

(2) Each element symbol is followed by a &#39;count&#39; number. A
   count of &#39;1&#39; may be omitted.

(3) A space or parenthesis must separate each cluster of (element
   symbol + count).

(4) Where a group of elements is enclosed in parentheses, the
   multiplier for the group must follow the closing parenthesis.
   That is, all element and group multipliers are assumed to be
   printed as subscripted numbers. (An exception to this rule
   exists for \*\_moiety formulae where pre- and post-multipliers
   are permitted for molecular units.)

(5) Unless the elements are ordered in a manner that corresponds
   to their chemical structure, as in
   [\_chemical\_formula\_structural](#_chemical_formula_structural), the order of the elements within
   any group or moiety depends on whether carbon is present or
   not. If carbon is present, the order should be: C, then H,
   then the other elements in alphabetical order of their
   symbol. If carbon is not present, the elements are listed
   purely in alphabetical order of their symbol. This is the
   &#39;Hill&#39; system used by Chemical Abstracts. This ordering is
   used in [\_chemical\_formula\_moiety](#_chemical_formula_moiety) and [\_chemical\_formula\_sum](#_chemical_formula_sum).

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
_chemical_formula_moiety            &#39;C18 H25 N O3&#39;
_chemical_formula_sum               &#39;C18 H25 N O3&#39;
_chemical_formula_weight            303.40
</code></pre>
  </td><td>Example 1 - based on data set TOZ of Willis, Beckwith &amp; Tozer
            [Acta Cryst. (1991), C47, 2276-2277].
  </td></tr>
  <tr><td>
<pre><code>
_chemical_formula_iupac      &#39;[Mo (C O)4 (C18 H33 P)2]&#39;
_chemical_formula_moiety     &#39;C40 H66 Mo O4 P2&#39;
_chemical_formula_structural &#39;((C O)4 (P (C6 H11)3)2)Mo&#39;
_chemical_formula_sum         &#39;C40 H66 Mo O4 P2&#39;
_chemical_formula_weight      768.81
</code></pre>
  </td><td>Example 2 - based on data set 9597gaus of Alyea, Ferguson &amp; Kannan
            [Acta Cryst. (1996), C52, 765-767].
  </td></tr>
</table>
### <a name="_chemical_formula_analytical"></a>\_chemical\_formula\_analytical

Formula determined by standard chemical analysis including trace
 elements. See the [\_chemical\_formula](#_chemical_formula)\_[] category description for 
 rules for writing chemical formulae. Parentheses are used only 
 for standard uncertainties (e.s.d.&#39;s).

### <a name="_chemical_formula_iupac"></a>\_chemical\_formula\_iupac

Formula expressed in conformance with IUPAC rules for inorganic
 and metal-organic compounds where these conflict with the rules
 for any other [\_chemical\_formula](#_chemical_formula)\_ entries. Typically used for
 formatting a formula in accordance with journal rules. This
 should appear in the data block in addition to the most
 appropriate of the other [\_chemical\_formula](#_chemical_formula)\_ data names.

 Ref: IUPAC (1990). Nomenclature of Inorganic Chemistry.
      Oxford: Blackwell Scientific Publications.

### <a name="_chemical_formula_moiety"></a>\_chemical\_formula\_moiety

Formula with each discrete bonded residue or ion shown as a
 separate moiety. See the [\_chemical\_formula](#_chemical_formula)\_[] category 
 description for rules for writing chemical formulae. In addition 
 to the general formulae requirements, the following rules apply:
    (1) Moieties are separated by commas &#39;,&#39;.
    (2) The order of elements within a moiety follows general rule
       (5) in the [\_chemical\_formula](#_chemical_formula)\_[] category description.
    (3) Parentheses are not used within moieties but may surround
       a moiety. Parentheses may not be nested.
    (4) Charges should be placed at the end of the moiety. The
       charge &#39;+&#39; or &#39;-&#39; may be preceded by a numerical multiplier
       and should be separated from the last (element symbol +
       count) by a space. Pre- or post-multipliers may be used for
       individual moieties.

### <a name="_chemical_formula_structural"></a>\_chemical\_formula\_structural

See the [\_chemical\_formula](#_chemical_formula)\_[] category description for the rules 
 for writing chemical formulae for inorganics, organometallics, 
 metal complexes etc., in which  bonded groups are preserved 
 as discrete entities within parentheses, with post-multipliers
 as required. The order of the elements should give as much
 information as possible about the chemical structure.
 Parentheses may be used and nested as required. This formula
 should correspond to the structure as actually reported,
 i.e. trace elements not included in atom-type and atom-site
 lists should not be included in this formula (see also
 [\_chemical\_formula\_analytical](#_chemical_formula_analytical)).

### <a name="_chemical_formula_sum"></a>\_chemical\_formula\_sum

See the [\_chemical\_formula](#_chemical_formula)\_[] category description for the rules 
 for writing chemical formulae in which all discrete bonded 
 residues and ions are summed over the constituent elements, 
 following the ordering given in general rule (5) in the 
 [\_chemical\_formula](#_chemical_formula)\_[] category description. Parentheses are not 
 normally used.

### <a name="_chemical_formula_weight"></a>\_chemical\_formula\_weight

Formula mass in daltons. This mass should correspond to the
 formulae given under [\_chemical\_formula\_structural](#_chemical_formula_structural), \*\_iupac,
 \*\_moiety or \*\_sum and, together with the Z value and cell
 parameters, should yield the density given as
 [\_exptl\_crystal\_density\_diffrn](#_exptl_crystal_density_diffrn).

Units: daltons

### <a name="_chemical_formula_weight_meas"></a>\_chemical\_formula\_weight\_meas

Formula mass in daltons measured by a non-diffraction experiment.

Units: daltons

## <a name="CITATION"></a>CITATION

Data items in the CITATION category record details about the
 literature cited as being relevant to the contents of the data
 block.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
_citation_id
_citation_coordinate_linkage
_citation_title
_citation_country
_citation_page_first
_citation_page_last
_citation_year
_citation_journal_abbrev
_citation_journal_volume
_citation_journal_issue
_citation_journal_id_ASTM
_citation_journal_id_ISSN
_citation_book_title
_citation_book_publisher
_citation_book_id_ISBN
_citation_special_details
  primary  yes
; Crystallographic analysis of a complex between human
  immunodeficiency virus type 1 protease and
  acetyl-pepstatin at 2.0-Angstroms resolution.
;
  US  14209  14219  1990  &#39;J. Biol. Chem.&#39;  265  .
  HBCHA3  0021-9258  .  .  .
; The publication that directly relates to this coordinate
  set.
;
  2  no
; Three-dimensional structure of aspartyl-protease from
  human immunodeficiency virus HIV-1.
;
  UK  615  619  1989  &#39;Nature&#39;  337  .
  NATUAS  0028-0836  .  .  .
; Determination of the structure of the unliganded enzyme.
;
  3 no
; Crystallization of the aspartylprotease from human
  immunodeficiency virus, HIV-1.
;
  US  1919  1921  1989  &#39;J. Biol. Chem.&#39;  264  .
  HBCHA3  0021-9258  .  .  .
; Crystallization of the unliganded enzyme.
;
</code></pre>
  </td><td>Example 1 - based on PDB entry 5HVP and laboratory records for the
            structure corresponding to PDB entry 5HVP.
  </td></tr>
</table>
### <a name="_citation_abstract"></a>\_citation\_abstract

Abstract for the citation. This is used most when the
 citation is extracted from a bibliographic database that
 contains full text or abstract information.

### <a name="_citation_abstract_id_CAS"></a>\_citation\_abstract\_id\_CAS

The Chemical Abstracts Service (CAS) abstract identifier;
 relevant for journal articles.

### <a name="_citation_book_id_ISBN"></a>\_citation\_book\_id\_ISBN

The International Standard Book Number (ISBN) code assigned to
 the book cited;  relevant for books or book chapters.

### <a name="_citation_book_publisher"></a>\_citation\_book\_publisher

The name of the publisher of the citation; relevant
 for books or book chapters.

### <a name="_citation_book_publisher_city"></a>\_citation\_book\_publisher\_city

The location of the publisher of the citation; relevant
 for books or book chapters.

### <a name="_citation_book_title"></a>\_citation\_book\_title

The title of the book in which the citation appeared;  relevant
 for books or book chapters.

### <a name="_citation_coordinate_linkage"></a>\_citation\_coordinate\_linkage

[\_citation\_coordinate\_linkage](#_citation_coordinate_linkage) states whether or not this citation
 is concerned with precisely the set of coordinates given in the
 data block. If, for instance, the publication described the same
 structure, but the coordinates had undergone further refinement
 prior to creation of the data block, the value of this data item
 would be &#39;no&#39;.

Values:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>no</td><td>citation unrelated to current coordinates</td></tr>
  <tr><td>n</td><td>abbreviation for &quot;no&quot;</td></tr>
  <tr><td>yes</td><td>citation related to current coordinates</td></tr>
  <tr><td>y</td><td>abbreviation for &quot;yes&quot;</td></tr>
</table>
### <a name="_citation_country"></a>\_citation\_country

The country of publication;  relevant for books and book
 chapters.

### <a name="_citation_database_id_CSD"></a>\_citation\_database\_id\_CSD

Identifier (&#39;refcode&#39;) of the database record in the Cambridge
 Structural Database that contains details of the cited structure.

### <a name="_citation_database_id_Medline"></a>\_citation\_database\_id\_Medline

Accession number used by Medline to categorize a specific
 bibliographic entry.

### <a name="_citation_id"></a>\_citation\_id

The value of [\_citation\_id](#_citation_id) must uniquely identify a record in the
 [\_citation](#_citation)\_ list.

 The [\_citation\_id](#_citation_id) &#39;primary&#39; should be used to indicate the
 citation that the author(s) consider to be the most pertinent to
 the contents of the data block.

 Note that this item need not be a number;  it can be any unique
 identifier.

### <a name="_citation_journal_abbrev"></a>\_citation\_journal\_abbrev

Abbreviated name of the journal cited as given in the Chemical
 Abstracts Service Source Index.

### <a name="_citation_journal_full"></a>\_citation\_journal\_full

Full name of the journal cited; relevant for journal articles.

### <a name="_citation_journal_id_ASTM"></a>\_citation\_journal\_id\_ASTM

The American Society for Testing and Materials (ASTM) code
 assigned to the journal cited (also referred to as the CODEN
 designator of the Chemical Abstracts Service); relevant for
 journal articles.

### <a name="_citation_journal_id_CSD"></a>\_citation\_journal\_id\_CSD

The Cambridge Structural Database (CSD) code assigned to the
 journal cited; relevant for journal articles. This is also the
 system used at the Protein Data Bank (PDB).

### <a name="_citation_journal_id_ISSN"></a>\_citation\_journal\_id\_ISSN

The International Standard Serial Number (ISSN) code assigned to
 the journal cited;  relevant for journal articles.

### <a name="_citation_journal_issue"></a>\_citation\_journal\_issue

Issue number of the journal cited;  relevant for journal
 articles.

### <a name="_citation_journal_volume"></a>\_citation\_journal\_volume

Volume number of the journal cited;  relevant for journal
 articles.

### <a name="_citation_language"></a>\_citation\_language

Language in which the cited article is written.

### <a name="_citation_page_first"></a>\_citation\_page\_first

The first and last pages of the citation;  relevant for
 journal articles, books and book chapters.

### <a name="_citation_page_last"></a>\_citation\_page\_last

The first and last pages of the citation;  relevant for
 journal articles, books and book chapters.

### <a name="_citation_special_details"></a>\_citation\_special\_details

A description of special aspects of the relationship
 of the contents of the data block to the literature item cited.

### <a name="_citation_title"></a>\_citation\_title

The title of the citation;  relevant for journal articles, books
 and book chapters.

### <a name="_citation_year"></a>\_citation\_year

The year of the citation;  relevant for journal articles, books
 and book chapters.

## <a name="CITATION_AUTHOR"></a>CITATION\_AUTHOR

Data items in the CITATION\_AUTHOR category record details
 about the authors associated with the citations in the
 [\_citation](#_citation)\_ list.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
_citation_author_citation_id
_citation_author_name
  primary  &#39;Fitzgerald, P.M.D.&#39;
  primary  &#39;McKeever, B.M.&#39;
  primary  &#39;Van Middlesworth, J.F.&#39;
  primary  &#39;Springer, J.P.&#39;
  primary  &#39;Heimbach, J.C.&#39;
  primary  &#39;Leu, C.-T.&#39;
  primary  &#39;Herber, W.K.&#39;
  primary  &#39;Dixon, R.A.F.&#39;
  primary  &#39;Darke, P.L.&#39;
  2        &#39;Navia, M.A.&#39;
  2        &#39;Fitzgerald, P.M.D.&#39;
  2        &#39;McKeever, B.M.&#39;
  2        &#39;Leu, C.-T.&#39;
  2        &#39;Heimbach, J.C.&#39;
  2        &#39;Herber, W.K.&#39;
  2        &#39;Sigal, I.S.&#39;
  2        &#39;Darke, P.L.&#39;
  2        &#39;Springer, J.P.&#39;
  3        &#39;McKeever, B.M.&#39;
  3        &#39;Navia, M.A.&#39;
  3        &#39;Fitzgerald, P.M.D.&#39;
  3        &#39;Springer, J.P.&#39;
  3        &#39;Leu, C.-T.&#39;
  3        &#39;Heimbach, J.C.&#39;
  3        &#39;Herber, W.K.&#39;
  3        &#39;Sigal, I.S.&#39;
  3        &#39;Darke, P.L.&#39;
</code></pre>
  </td><td>Example 1 - based on PDB entry 5HVP and laboratory records for the
            structure corresponding to PDB entry 5HVP.
  </td></tr>
</table>
### <a name="_citation_author_citation_id"></a>\_citation\_author\_citation\_id

The value of [\_citation\_author\_citation\_id](#_citation_author_citation_id) must match an
 identifier specified by [\_citation\_id](#_citation_id) in the [\_citation](#_citation)\_ list.

### <a name="_citation_author_name"></a>\_citation\_author\_name

Name of an author of the citation; relevant for journal
 articles, books and book chapters.

 The family name(s), followed by a comma and including any
 dynastic components, precedes the first name(s) or initial(s).

### <a name="_citation_author_ordinal"></a>\_citation\_author\_ordinal

This data name defines the order of the author&#39;s name in the
 list of authors of a citation.

## <a name="CITATION_EDITOR"></a>CITATION\_EDITOR

Data items in the CITATION\_EDITOR category record details
 about the editor associated with the book or book chapter
 citations in the [\_citation](#_citation)\_ list.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
_citation_editor_citation_id
_citation_editor_name
  5        &#39;McKeever, B.M.&#39;
  5        &#39;Navia, M.A.&#39;
  5        &#39;Fitzgerald, P.M.D.&#39;
  5        &#39;Springer, J.P.&#39;
</code></pre>
  </td><td>Example 1 - hypothetical example.
  </td></tr>
</table>
### <a name="_citation_editor_citation_id"></a>\_citation\_editor\_citation\_id

The value of [\_citation\_editor\_citation\_id](#_citation_editor_citation_id) must match an
 identifier specified by [\_citation\_id](#_citation_id) in the [\_citation](#_citation)\_ list.

### <a name="_citation_editor_name"></a>\_citation\_editor\_name

Name of an editor of the citation;  relevant for books and
 book chapters.

 The family name(s), followed by a comma and including any
 dynastic components, precedes the first name(s) or initial(s).

### <a name="_citation_editor_ordinal"></a>\_citation\_editor\_ordinal

This data name defines the order of the editor&#39;s name in the
 list of editors of a citation.

## <a name="COMPUTING"></a>COMPUTING

Data items in the COMPUTING category record details about the
 computer programs used in the crystal structure analysis.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
_computing_data_collection       &#39;CAD-4 (Enraf-Nonius, 1989)&#39;
_computing_cell_refinement       &#39;CAD-4 (Enraf-Nonius, 1989)&#39;
_computing_data_reduction        &#39;CFEO (Solans, 1978)&#39;
_computing_structure_solution    &#39;SHELXS86 (Sheldrick, 1990)&#39;
_computing_structure_refinement  &#39;SHELXL93 (Sheldrick, 1993)&#39;
_computing_molecular_graphics    &#39;ORTEPII (Johnson, 1976)&#39;
_computing_publication_material  &#39;PARST (Nardelli, 1983)&#39;
</code></pre>
  </td><td>Example 1 - Rodr&iacute;guez-Romero, Ruiz-P&eacute;rez &amp; Solans
            [Acta Cryst. (1996), C52, 1415-1417].
  </td></tr>
</table>
### <a name="_computing_cell_refinement"></a>\_computing\_cell\_refinement

Software used in the processing of the data. Give the program
 or package name and a brief reference.

### <a name="_computing_data_collection"></a>\_computing\_data\_collection

Software used in the processing of the data. Give the program
 or package name and a brief reference.

### <a name="_computing_data_reduction"></a>\_computing\_data\_reduction

Software used in the processing of the data. Give the program
 or package name and a brief reference.

### <a name="_computing_molecular_graphics"></a>\_computing\_molecular\_graphics

Software used in the processing of the data. Give the program
 or package name and a brief reference.

### <a name="_computing_publication_material"></a>\_computing\_publication\_material

Software used in the processing of the data. Give the program
 or package name and a brief reference.

### <a name="_computing_structure_refinement"></a>\_computing\_structure\_refinement

Software used in the processing of the data. Give the program
 or package name and a brief reference.

### <a name="_computing_structure_solution"></a>\_computing\_structure\_solution

Software used in the processing of the data. Give the program
 or package name and a brief reference.

## <a name="DATABASE"></a>DATABASE

Data items in the DATABASE category record details about the
 database identifiers of the data block.

 These data items are assigned by database managers and should
 only appear in a CIF if they originate from that source.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
_database_code_CSD                  &#39;VOBYUG&#39;
  </td><td>Example 1 - based on data set TOZ of Willis, Beckwith &amp; Tozer
            [Acta Cryst. (1991), C47, 2276-2277].
  </td></tr>
</table>
### <a name="_database_code_CAS"></a>\_database\_code\_CAS

The codes are assigned by databases: Chemical Abstracts;
 Cambridge Structural Database (organic and metal-organic
 compounds); Inorganic Crystal Structure Database; Metals
 Data File (metal structures); NBS (NIST) Crystal Data
 Database (lattice parameters); Protein Data Bank; and the
 Powder Diffraction File (JCPDS/ICDD).

### <a name="_database_code_CSD"></a>\_database\_code\_CSD

The codes are assigned by databases: Chemical Abstracts;
 Cambridge Structural Database (organic and metal-organic
 compounds); Inorganic Crystal Structure Database; Metals
 Data File (metal structures); NBS (NIST) Crystal Data
 Database (lattice parameters); Protein Data Bank; and the
 Powder Diffraction File (JCPDS/ICDD).

### <a name="_database_code_ICSD"></a>\_database\_code\_ICSD

The codes are assigned by databases: Chemical Abstracts;
 Cambridge Structural Database (organic and metal-organic
 compounds); Inorganic Crystal Structure Database; Metals
 Data File (metal structures); NBS (NIST) Crystal Data
 Database (lattice parameters); Protein Data Bank; and the
 Powder Diffraction File (JCPDS/ICDD).

### <a name="_database_code_MDF"></a>\_database\_code\_MDF

The codes are assigned by databases: Chemical Abstracts;
 Cambridge Structural Database (organic and metal-organic
 compounds); Inorganic Crystal Structure Database; Metals
 Data File (metal structures); NBS (NIST) Crystal Data
 Database (lattice parameters); Protein Data Bank; and the
 Powder Diffraction File (JCPDS/ICDD).

### <a name="_database_code_NBS"></a>\_database\_code\_NBS

The codes are assigned by databases: Chemical Abstracts;
 Cambridge Structural Database (organic and metal-organic
 compounds); Inorganic Crystal Structure Database; Metals
 Data File (metal structures); NBS (NIST) Crystal Data
 Database (lattice parameters); Protein Data Bank; and the
 Powder Diffraction File (JCPDS/ICDD).

### <a name="_database_code_PDB"></a>\_database\_code\_PDB

The codes are assigned by databases: Chemical Abstracts;
 Cambridge Structural Database (organic and metal-organic
 compounds); Inorganic Crystal Structure Database; Metals
 Data File (metal structures); NBS (NIST) Crystal Data
 Database (lattice parameters); Protein Data Bank; and the
 Powder Diffraction File (JCPDS/ICDD).

### <a name="_database_code_PDF"></a>\_database\_code\_PDF

The codes are assigned by databases: Chemical Abstracts;
 Cambridge Structural Database (organic and metal-organic
 compounds); Inorganic Crystal Structure Database; Metals
 Data File (metal structures); NBS (NIST) Crystal Data
 Database (lattice parameters); Protein Data Bank; and the
 Powder Diffraction File (JCPDS/ICDD).

### <a name="_database_code_depnum_ccdc_archive"></a>\_database\_code\_depnum\_ccdc\_archive

Deposition numbers assigned by the Cambridge Crystallographic
 Data Centre (CCDC) to files containing structural information
 archived by the CCDC.

### <a name="_database_code_depnum_ccdc_fiz"></a>\_database\_code\_depnum\_ccdc\_fiz

Deposition numbers assigned by the Fachinformationszentrum
 Karlsruhe (FIZ) to files containing structural information
 archived by the Cambridge Crystallographic Data Centre (CCDC).

### <a name="_database_code_depnum_ccdc_journal"></a>\_database\_code\_depnum\_ccdc\_journal

Deposition numbers assigned by various journals to files
 containing structural information archived by the Cambridge
 Crystallographic Data Centre (CCDC).

### <a name="_database_CSD_history"></a>\_database\_CSD\_history

A history of changes made by the Cambridge Crystallographic Data
 Centre and incorporated into the Cambridge Structural Database
 (CSD).

### <a name="_database_journal_ASTM"></a>\_database\_journal\_ASTM

The ASTM CODEN designator for a journal as given in the
 Chemical Source List maintained by the Chemical Abstracts
 Service, and the journal code used in the Cambridge Structural
 Database.

### <a name="_database_journal_CSD"></a>\_database\_journal\_CSD

The ASTM CODEN designator for a journal as given in the
 Chemical Source List maintained by the Chemical Abstracts
 Service, and the journal code used in the Cambridge Structural
 Database.

## <a name="DIFFRN"></a>DIFFRN

Data items in the DIFFRN category record details about the
 intensity measurements.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
_diffrn_special_details
; &theta; scan width (1.0 + 0.14tan&theta;)&deg;, &theta; scan rate
  1.2&deg; min^-1^. Background counts for 5 s on each side
  every scan.
;

_diffrn_ambient_temperature         293
</code></pre>
  </td><td>Example 1 - based on data set TOZ of Willis, Beckwith &amp; Tozer
            [Acta Cryst. (1991), C47, 2276-2277].
  </td></tr>
</table>
### <a name="_diffrn_ambient_environment"></a>\_diffrn\_ambient\_environment

The gas or liquid surrounding the sample, if not air.

### <a name="_diffrn_ambient_pressure"></a>\_diffrn\_ambient\_pressure

The mean hydrostatic pressure in kilopascals at which the
 intensities were measured.

Units: kilopascals

### <a name="_diffrn_ambient_pressure_gt"></a>\_diffrn\_ambient\_pressure\_gt

The mean hydrostatic pressure in kilopascals above which (\*\_gt)
 or below which (\*\_lt) the intensities were measured. These
 items allow for a pressure range to be given.

 [\_diffrn\_ambient\_pressure](#_diffrn_ambient_pressure) should always be used in
 preference to these items whenever possible.

Units: kilopascals

### <a name="_diffrn_ambient_pressure_lt"></a>\_diffrn\_ambient\_pressure\_lt

The mean hydrostatic pressure in kilopascals above which (\*\_gt)
 or below which (\*\_lt) the intensities were measured. These
 items allow for a pressure range to be given.

 [\_diffrn\_ambient\_pressure](#_diffrn_ambient_pressure) should always be used in
 preference to these items whenever possible.

Units: kilopascals

### <a name="_diffrn_ambient_temperature"></a>\_diffrn\_ambient\_temperature

The mean temperature in kelvins at which the intensities
 were measured.

Units: kelvin

### <a name="_diffrn_ambient_temperature_gt"></a>\_diffrn\_ambient\_temperature\_gt

The mean temperature in kelvins above which (\*\_gt) or below
 which (\*\_lt) the intensities were measured.  These items allow
 a range of temperatures to be given.

 [\_diffrn\_ambient\_temperature](#_diffrn_ambient_temperature) should always be used in preference
 to these items whenever possible.

Units: kelvin

### <a name="_diffrn_ambient_temperature_lt"></a>\_diffrn\_ambient\_temperature\_lt

The mean temperature in kelvins above which (\*\_gt) or below
 which (\*\_lt) the intensities were measured.  These items allow
 a range of temperatures to be given.

 [\_diffrn\_ambient\_temperature](#_diffrn_ambient_temperature) should always be used in preference
 to these items whenever possible.

Units: kelvin

### <a name="_diffrn_crystal_treatment"></a>\_diffrn\_crystal\_treatment

Remarks about how the crystal was treated prior to the intensity
 measurements. Particularly relevant when intensities were
 measured at low temperature.

### <a name="_diffrn_measured_fraction_theta_full"></a>\_diffrn\_measured\_fraction\_theta\_full

Fraction of unique (symmetry-independent) reflections measured
 out to [\_diffrn\_reflns\_theta\_full](#_diffrn_reflns_theta_full).

### <a name="_diffrn_measured_fraction_theta_max"></a>\_diffrn\_measured\_fraction\_theta\_max

Fraction of unique (symmetry-independent) reflections measured
 out to [\_diffrn\_reflns\_theta\_max](#_diffrn_reflns_theta_max).

### <a name="_diffrn_special_details"></a>\_diffrn\_special\_details

Special details of the intensity-measurement process. Should
 include information about source instability, crystal motion,
 degradation and so on.

### <a name="_diffrn_symmetry_description"></a>\_diffrn\_symmetry\_description

Observed diffraction point symmetry, systematic absences and
 possible space group(s) or superspace group(s) compatible with
 these.

## <a name="DIFFRN_ATTENUATOR"></a>DIFFRN\_ATTENUATOR

Data items in the DIFFRN\_ATTENUATOR category record details
 about the diffraction attenuator scales employed.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
  _diffrn_attenuator_code
  _diffrn_attenuator_scale       
      0         1.00
      1        16.97
      2        33.89
</code></pre>
  </td><td>Example 1 - hypothetical example.
  </td></tr>
</table>
### <a name="_diffrn_attenuator_code"></a>\_diffrn\_attenuator\_code

A code associated with a particular attenuator setting. This code
 is referenced by the [\_diffrn\_refln\_attenuator\_code](#_diffrn_refln_attenuator_code) which is
 stored with the intensities. See [\_diffrn\_attenuator\_scale](#_diffrn_attenuator_scale).

### <a name="_diffrn_attenuator_material"></a>\_diffrn\_attenuator\_material

Material from which the attenuator is made.

### <a name="_diffrn_attenuator_scale"></a>\_diffrn\_attenuator\_scale

The scale factor applied when an intensity measurement is
 reduced by an attenuator identified by [\_diffrn\_attenuator\_code](#_diffrn_attenuator_code).
 The measured intensity must be multiplied by this scale to
 convert it to the same scale as unattenuated intensities.

## <a name="DIFFRN_DETECTOR"></a>DIFFRN\_DETECTOR

Data items in the DIFFRN\_DETECTOR category describe the
 detector used to measure the scattered radiation, including
 any analyser and post-sample collimation.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
_diffrn_detector                    &#39;multiwire&#39;
_diffrn_detector_type               &#39;Siemens&#39;
</code></pre>
  </td><td>Example 1 - based on PDB entry 5HVP and laboratory records for the
            structure corresponding to PDB entry 5HVP.
  </td></tr>
</table>
### <a name="_diffrn_detector"></a>\_diffrn\_detector

The general class of the radiation detector.

### <a name="_diffrn_detector_area_resol_mean"></a>\_diffrn\_detector\_area\_resol\_mean

The resolution of an area detector, in pixels/mm.

Units: pixels\_per\_millimetre

### <a name="_diffrn_detector_details"></a>\_diffrn\_detector\_details

A description of special aspects of the radiation detector.

### <a name="_diffrn_detector_dtime"></a>\_diffrn\_detector\_dtime

The deadtime in microseconds of the detector used to measure
 the diffraction intensities.

### <a name="_diffrn_detector_type"></a>\_diffrn\_detector\_type

The make, model or name of the detector device used.

### <a name="_diffrn_radiation_detector"></a>\_diffrn\_radiation\_detector

The detector used to measure the diffraction intensities.

### <a name="_diffrn_radiation_detector_dtime"></a>\_diffrn\_radiation\_detector\_dtime

The deadtime in microseconds of the detector used to measure
 the diffraction intensities.

## <a name="DIFFRN_MEASUREMENT"></a>DIFFRN\_MEASUREMENT

Data items in the DIFFRN\_MEASUREMENT category refer to the
 mounting of the sample and to the goniometer on which it is
 mounted.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
_diffrn_measurement_device_type
                          &#39;Philips PW1100/20 diffractometer&#39;
_diffrn_measurement_method          &theta;/2&theta;
</code></pre>
  </td><td>Example 1 - based on data set TOZ of Willis, Beckwith &amp; Tozer
            [Acta Cryst. (1991), C47, 2276-2277].
  </td></tr>
</table>
### <a name="_diffrn_measurement_details"></a>\_diffrn\_measurement\_details

A description of special aspects of the intensity measurement.

### <a name="_diffrn_measurement_device"></a>\_diffrn\_measurement\_device

The general class of goniometer or device used to support
 and orient the specimen.

### <a name="_diffrn_measurement_device_details"></a>\_diffrn\_measurement\_device\_details

A description of special aspects of the device used to measure
 the diffraction intensities.

### <a name="_diffrn_measurement_device_type"></a>\_diffrn\_measurement\_device\_type

The make, model or name of the measurement device
 (goniometer) used.

### <a name="_diffrn_measurement_method"></a>\_diffrn\_measurement\_method

Method used to measure the intensities.

### <a name="_diffrn_measurement_specimen_support"></a>\_diffrn\_measurement\_specimen\_support

The physical device used to support the crystal during data
 collection.

## <a name="DIFFRN_ORIENT_MATRIX"></a>DIFFRN\_ORIENT\_MATRIX

Data items in the DIFFRN\_ORIENT\_MATRIX category record details
 about the orientation matrix used in the measurement of the
 diffraction intensities.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
_diffrn_orient_matrix_UB_11           -0.04170
_diffrn_orient_matrix_UB_12           -0.01429
_diffrn_orient_matrix_UB_13           -0.02226
_diffrn_orient_matrix_UB_21           -0.00380
_diffrn_orient_matrix_UB_22           -0.05578
_diffrn_orient_matrix_UB_23           -0.05048
_diffrn_orient_matrix_UB_31            0.00587
_diffrn_orient_matrix_UB_32           -0.13766
_diffrn_orient_matrix_UB_33            0.02277

_diffrn_orient_matrix_type &#39;TEXSAN convention (MSC, 1989)&#39;
</code></pre>
  </td><td>Example 1 - data set n-alkylation_C-4 of Hussain, Fleming, Norman &amp; Chang
            [Acta Cryst. (1996), C52, 1010-1012].
  </td></tr>
</table>
### <a name="_diffrn_orient_matrix_type"></a>\_diffrn\_orient\_matrix\_type

A description of the orientation matrix type and how it should
 be applied to define the orientation of the crystal precisely
 with respect to the diffractometer axes.

### <a name="_diffrn_orient_matrix_UB_11"></a>\_diffrn\_orient\_matrix\_UB\_11

The elements of the diffractometer orientation matrix. These
 define the dimensions of the reciprocal cell and its orientation
 to the local diffractometer axes. See [\_diffrn\_orient\_matrix\_type](#_diffrn_orient_matrix_type).

### <a name="_diffrn_orient_matrix_UB_12"></a>\_diffrn\_orient\_matrix\_UB\_12

The elements of the diffractometer orientation matrix. These
 define the dimensions of the reciprocal cell and its orientation
 to the local diffractometer axes. See [\_diffrn\_orient\_matrix\_type](#_diffrn_orient_matrix_type).

### <a name="_diffrn_orient_matrix_UB_13"></a>\_diffrn\_orient\_matrix\_UB\_13

The elements of the diffractometer orientation matrix. These
 define the dimensions of the reciprocal cell and its orientation
 to the local diffractometer axes. See [\_diffrn\_orient\_matrix\_type](#_diffrn_orient_matrix_type).

### <a name="_diffrn_orient_matrix_UB_21"></a>\_diffrn\_orient\_matrix\_UB\_21

The elements of the diffractometer orientation matrix. These
 define the dimensions of the reciprocal cell and its orientation
 to the local diffractometer axes. See [\_diffrn\_orient\_matrix\_type](#_diffrn_orient_matrix_type).

### <a name="_diffrn_orient_matrix_UB_22"></a>\_diffrn\_orient\_matrix\_UB\_22

The elements of the diffractometer orientation matrix. These
 define the dimensions of the reciprocal cell and its orientation
 to the local diffractometer axes. See [\_diffrn\_orient\_matrix\_type](#_diffrn_orient_matrix_type).

### <a name="_diffrn_orient_matrix_UB_23"></a>\_diffrn\_orient\_matrix\_UB\_23

The elements of the diffractometer orientation matrix. These
 define the dimensions of the reciprocal cell and its orientation
 to the local diffractometer axes. See [\_diffrn\_orient\_matrix\_type](#_diffrn_orient_matrix_type).

### <a name="_diffrn_orient_matrix_UB_31"></a>\_diffrn\_orient\_matrix\_UB\_31

The elements of the diffractometer orientation matrix. These
 define the dimensions of the reciprocal cell and its orientation
 to the local diffractometer axes. See [\_diffrn\_orient\_matrix\_type](#_diffrn_orient_matrix_type).

### <a name="_diffrn_orient_matrix_UB_32"></a>\_diffrn\_orient\_matrix\_UB\_32

The elements of the diffractometer orientation matrix. These
 define the dimensions of the reciprocal cell and its orientation
 to the local diffractometer axes. See [\_diffrn\_orient\_matrix\_type](#_diffrn_orient_matrix_type).

### <a name="_diffrn_orient_matrix_UB_33"></a>\_diffrn\_orient\_matrix\_UB\_33

The elements of the diffractometer orientation matrix. These
 define the dimensions of the reciprocal cell and its orientation
 to the local diffractometer axes. See [\_diffrn\_orient\_matrix\_type](#_diffrn_orient_matrix_type).

## <a name="DIFFRN_ORIENT_REFLN"></a>DIFFRN\_ORIENT\_REFLN

Data items in the DIFFRN\_ORIENT\_REFLN category record details
 about the reflections that define the orientation matrix used in
 the measurement of the diffraction intensities.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
_diffrn_orient_refln_index_h
_diffrn_orient_refln_index_k
_diffrn_orient_refln_index_l
_diffrn_orient_refln_angle_theta
_diffrn_orient_refln_angle_phi
_diffrn_orient_refln_angle_omega
_diffrn_orient_refln_angle_kappa
  -3   2   3    7.35   44.74   2.62    17.53
  -4   1   0    9.26   83.27   8.06     5.79
   0   0   6    5.85  -43.93 -25.36    86.20
   2   1   3    7.36  -57.87   6.26     5.42
   0   0  -6    5.85 -161.59  36.96   -86.79
  -3   1   0    6.74   80.28   5.87     2.60
   2   0   3    5.86  -76.86  -0.17    21.34
   0   0  12   11.78  -44.02 -19.51    86.41
   0   0 -12   11.78 -161.67  42.81   -86.61
  -5   1   0   11.75   86.24   9.16     7.44
   0   4   6   11.82  -19.82  10.45     4.19
   5   0   6   14.13  -77.28  10.17    15.34
   8   0   0   20.79  -77.08  25.30   -13.96
</code></pre>
  </td><td>Example 1 - typical output listing from an Enraf-Nonius CAD-4
diffractometer.
  </td></tr>
</table>
### <a name="_diffrn_orient_refln_angle_chi"></a>\_diffrn\_orient\_refln\_angle\_chi

Diffractometer angles of a reflection used to define
 the orientation matrix in degrees. See
 \_diffrn\_orient\_matrix\_UB\_ and
 [\_diffrn\_orient\_refln\_index\_h](#_diffrn_orient_refln_index_h), \*\_k and \*\_l.

Units: degrees

### <a name="_diffrn_orient_refln_angle_kappa"></a>\_diffrn\_orient\_refln\_angle\_kappa

Diffractometer angles of a reflection used to define
 the orientation matrix in degrees. See
 \_diffrn\_orient\_matrix\_UB\_ and
 [\_diffrn\_orient\_refln\_index\_h](#_diffrn_orient_refln_index_h), \*\_k and \*\_l.

Units: degrees

### <a name="_diffrn_orient_refln_angle_omega"></a>\_diffrn\_orient\_refln\_angle\_omega

Diffractometer angles of a reflection used to define
 the orientation matrix in degrees. See
 \_diffrn\_orient\_matrix\_UB\_ and
 [\_diffrn\_orient\_refln\_index\_h](#_diffrn_orient_refln_index_h), \*\_k and \*\_l.

Units: degrees

### <a name="_diffrn_orient_refln_angle_phi"></a>\_diffrn\_orient\_refln\_angle\_phi

Diffractometer angles of a reflection used to define
 the orientation matrix in degrees. See
 \_diffrn\_orient\_matrix\_UB\_ and
 [\_diffrn\_orient\_refln\_index\_h](#_diffrn_orient_refln_index_h), \*\_k and \*\_l.

Units: degrees

### <a name="_diffrn_orient_refln_angle_psi"></a>\_diffrn\_orient\_refln\_angle\_psi

Diffractometer angles of a reflection used to define
 the orientation matrix in degrees. See
 \_diffrn\_orient\_matrix\_UB\_ and
 [\_diffrn\_orient\_refln\_index\_h](#_diffrn_orient_refln_index_h), \*\_k and \*\_l.

Units: degrees

### <a name="_diffrn_orient_refln_angle_theta"></a>\_diffrn\_orient\_refln\_angle\_theta

Diffractometer angles of a reflection used to define
 the orientation matrix in degrees. See
 \_diffrn\_orient\_matrix\_UB\_ and
 [\_diffrn\_orient\_refln\_index\_h](#_diffrn_orient_refln_index_h), \*\_k and \*\_l.

Units: degrees

### <a name="_diffrn_orient_refln_index_h"></a>\_diffrn\_orient\_refln\_index\_h

The indices of a reflection used to define the orientation
 matrix. See [\_diffrn\_orient\_matrix](#_diffrn_orient_matrix)\_.

### <a name="_diffrn_orient_refln_index_k"></a>\_diffrn\_orient\_refln\_index\_k

The indices of a reflection used to define the orientation
 matrix. See [\_diffrn\_orient\_matrix](#_diffrn_orient_matrix)\_.

### <a name="_diffrn_orient_refln_index_l"></a>\_diffrn\_orient\_refln\_index\_l

The indices of a reflection used to define the orientation
 matrix. See [\_diffrn\_orient\_matrix](#_diffrn_orient_matrix)\_.

## <a name="DIFFRN_RADIATION"></a>DIFFRN\_RADIATION

Data items in the DIFFRN\_RADIATION category describe the
 radiation used in measuring the diffraction intensities, its
 collimation and monochromatization before the sample.

 Post-sample treatment of the beam is described by data items
 in the DIFFRN\_DETECTOR category.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
_diffrn_radiation_type             &#39;Cu K&alpha;&#39;
_diffrn_radiation_monochromator    &#39;graphite&#39;
</code></pre>
  </td><td>Example 1 - based on data set TOZ of Willis, Beckwith &amp; Tozer
            [Acta Cryst. (1991), C47, 2276-2277].
  </td></tr>
</table>
### <a name="_diffrn_radiation_collimation"></a>\_diffrn\_radiation\_collimation

The collimation or focusing applied to the radiation.

### <a name="_diffrn_radiation_filter_edge"></a>\_diffrn\_radiation\_filter\_edge

Absorption edge in angstroms of the radiation filter used.

Units: angstroms

### <a name="_diffrn_radiation_inhomogeneity"></a>\_diffrn\_radiation\_inhomogeneity

Half-width in millimetres of the incident beam in the
 direction perpendicular to the diffraction plane.

### <a name="_diffrn_radiation_monochromator"></a>\_diffrn\_radiation\_monochromator

The method used to obtain monochromatic radiation. If a mono-
 chromator crystal is used, the material and the indices of the
 Bragg reflection are specified.

### <a name="_diffrn_radiation_polarisn_norm"></a>\_diffrn\_radiation\_polarisn\_norm

The angle in degrees, as viewed from the specimen, between the
 perpendicular component of the polarization and the diffraction
 plane. See [\_diffrn\_radiation\_polarisn\_ratio](#_diffrn_radiation_polarisn_ratio).

Units: degrees

### <a name="_diffrn_radiation_polarisn_ratio"></a>\_diffrn\_radiation\_polarisn\_ratio

Polarization ratio of the diffraction beam incident on the
 crystal. It is the ratio of the perpendicularly polarized to the
 parallel polarized components of the radiation. The perpendicular
 component forms an angle of [\_diffrn\_radiation\_polarisn\_norm](#_diffrn_radiation_polarisn_norm) to
 the normal to the diffraction plane of the sample (i.e. the plane
 containing the incident and reflected beams).

### <a name="_diffrn_radiation_probe"></a>\_diffrn\_radiation\_probe

The nature of the radiation used (i.e. the name of the
 subatomic particle or the region of the electromagnetic
 spectrum). It is strongly recommended that this information
 be given, so that the probe radiation can be simply determined.

Values:

* x-ray
* neutron
* electron
* gamma

### <a name="_diffrn_radiation_type"></a>\_diffrn\_radiation\_type

The type of the radiation. This is used to give a more
 detailed description than [\_diffrn\_radiation\_probe](#_diffrn_radiation_probe) and is
 typically a description of the X-ray wavelength in Siegbahn
 notation.

### <a name="_diffrn_radiation_xray_symbol"></a>\_diffrn\_radiation\_xray\_symbol

The IUPAC symbol for the X-ray wavelength for the probe
 radiation.

Values:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>K-L~3~</td><td>K&alpha;~1~ in older Siegbahn notation</td></tr>
  <tr><td>K-L~2~</td><td>K&alpha;~2~ in older Siegbahn notation</td></tr>
  <tr><td>K-M~3~</td><td>K&beta;~1~ in older Siegbahn notation</td></tr>
  <tr><td>K-L~2,3~</td><td>use where K-L~3~ and K-L~2~ are not resolved</td></tr>
</table>
## <a name="DIFFRN_RADIATION_WAVELENGTH"></a>DIFFRN\_RADIATION\_WAVELENGTH

Data items in the DIFFRN\_RADIATION\_WAVELENGTH category describe
 the wavelength of the radiation used in measuring the diffraction
 intensities. Items may be looped to identify and assign weights
 to distinct wavelength components from a polychromatic beam.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
_diffrn_radiation_wavelength       1.5418
  </td><td>Example 1 - based on data set TOZ of Willis, Beckwith &amp; Tozer
            [Acta Cryst. (1991), C47, 2276-2277].
  </td></tr>
</table>
### <a name="_diffrn_radiation_wavelength"></a>\_diffrn\_radiation\_wavelength

The radiation wavelength in angstroms.

Units: angstroms

### <a name="_diffrn_radiation_wavelength_id"></a>\_diffrn\_radiation\_wavelength\_id

An arbitrary code identifying each value of
 [\_diffrn\_radiation\_wavelength](#_diffrn_radiation_wavelength). Items in the DIFFRN\_RADIATION
 category are looped when multiple wavelengths are used.
 This code is used to link with the [\_diffrn\_refln](#_diffrn_refln)\_ list. It
 must match with one of the [\_diffrn\_refln\_wavelength\_id](#_diffrn_refln_wavelength_id) codes.

### <a name="_diffrn_radiation_wavelength_wt"></a>\_diffrn\_radiation\_wavelength\_wt

The relative weight of a wavelength identified by the code
 [\_diffrn\_radiation\_wavelength\_id](#_diffrn_radiation_wavelength_id) in the list of wavelengths.

Default value: '1.0'

## <a name="DIFFRN_REFLN"></a>DIFFRN\_REFLN

Data items in the DIFFRN\_REFLN category record details about
 the intensities measured in the diffraction experiment.

 The DIFFRN\_REFLN data items refer to individual intensity
 measurements and must be included in looped lists.

 (The DIFFRN\_REFLNS data items specify the parameters that apply
 to all intensity  measurements. The DIFFRN\_REFLNS data items
 are not looped.)

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
    _diffrn_refln_index_h
    _diffrn_refln_index_k
    _diffrn_refln_index_l
    _diffrn_refln_angle_chi
    _diffrn_refln_scan_rate
    _diffrn_refln_counts_bg_1
    _diffrn_refln_counts_total
    _diffrn_refln_counts_bg_2
    _diffrn_refln_angle_theta
    _diffrn_refln_angle_phi
    _diffrn_refln_angle_omega
    _diffrn_refln_angle_kappa
    _diffrn_refln_scan_width
    _diffrn_refln_elapsed_time

 0  0 -16  0. 4.12  28 127  36  33.157  -75.846  16.404   50.170  1.516 19.43
 0  0 -15  0. 4.12  38 143  28  30.847  -75.846  14.094   50.170  1.516 19.82
 0  0 -14  0. 1.03 142 742 130  28.592  -75.846  11.839   50.170  1.516 21.32
 0  0 -13  0. 4.12  26 120  37  26.384  -75.846   9.631   50.170  1.450 21.68
 0  0 -12  0. 0.97 129 618 153  24.218  -75.846   7.464   50.170  1.450 23.20
 0  0 -11  0. 4.12  33 107  38  22.087  -75.846   5.334   50.170  1.384 23.55
 0  0 -10  0. 4.12  37 146  33  19.989  -75.846   3.235   50.170  1.384 23.90
 0  0  -9  0. 4.12  50 179  49  17.918  -75.846   1.164   50.170  1.384 24.25
# - - - - data truncated for brevity - - - -
 3  4  -4  0. 1.03  69 459  73  30.726  -53.744  46.543  -47.552  1.516 2082.58
 3  4  -5  0. 1.03  91 465  75  31.407  -54.811  45.519  -42.705  1.516 2084.07
 3 14  -6  0. 1.03  84 560  79  32.228  -55.841  44.745  -38.092  1.516 2085.57
# - - - - data truncated for brevity - - - -
</code></pre>
  </td><td>Example 1 - extracted from the CAD-4 listing for Tl~2~Cd~2~(SO~4~)~3~ at
            85 K (unpublished).
  </td></tr>
</table>
### <a name="_diffrn_refln_angle_chi"></a>\_diffrn\_refln\_angle\_chi

The diffractometer angles of a reflection in degrees. These
 correspond to the specified orientation matrix and the original
 measured cell before any subsequent cell transformations.

Units: degrees

### <a name="_diffrn_refln_angle_kappa"></a>\_diffrn\_refln\_angle\_kappa

The diffractometer angles of a reflection in degrees. These
 correspond to the specified orientation matrix and the original
 measured cell before any subsequent cell transformations.

Units: degrees

### <a name="_diffrn_refln_angle_omega"></a>\_diffrn\_refln\_angle\_omega

The diffractometer angles of a reflection in degrees. These
 correspond to the specified orientation matrix and the original
 measured cell before any subsequent cell transformations.

Units: degrees

### <a name="_diffrn_refln_angle_phi"></a>\_diffrn\_refln\_angle\_phi

The diffractometer angles of a reflection in degrees. These
 correspond to the specified orientation matrix and the original
 measured cell before any subsequent cell transformations.

Units: degrees

### <a name="_diffrn_refln_angle_psi"></a>\_diffrn\_refln\_angle\_psi

The diffractometer angles of a reflection in degrees. These
 correspond to the specified orientation matrix and the original
 measured cell before any subsequent cell transformations.

Units: degrees

### <a name="_diffrn_refln_angle_theta"></a>\_diffrn\_refln\_angle\_theta

The diffractometer angles of a reflection in degrees. These
 correspond to the specified orientation matrix and the original
 measured cell before any subsequent cell transformations.

Units: degrees

### <a name="_diffrn_refln_attenuator_code"></a>\_diffrn\_refln\_attenuator\_code

The code identifying the attenuator setting for this reflection.
 This code must match one of the [\_diffrn\_attenuator\_code](#_diffrn_attenuator_code) values.

### <a name="_diffrn_refln_class_code"></a>\_diffrn\_refln\_class\_code

The code identifying the class to which this reflection has
 been assigned. This code must match a value of
 [\_diffrn\_reflns\_class\_code](#_diffrn_reflns_class_code). Reflections may be grouped into
 classes for a variety of purposes. For example, for modulated
 structures each reflection class may be defined by the
 number m=sum|m~i~|, where the m~i~ are the integer coefficients
 that, in addition to h,k,l, index the corresponding diffraction
 vector in the basis defined for the reciprocal lattice.

### <a name="_diffrn_refln_counts_bg_1"></a>\_diffrn\_refln\_counts\_bg\_1

The diffractometer counts for the measurements: background
 before the peak, background after the peak, net counts after
 background removed, counts for peak scan or position, and the
 total counts (background plus peak).

### <a name="_diffrn_refln_counts_bg_2"></a>\_diffrn\_refln\_counts\_bg\_2

The diffractometer counts for the measurements: background
 before the peak, background after the peak, net counts after
 background removed, counts for peak scan or position, and the
 total counts (background plus peak).

### <a name="_diffrn_refln_counts_net"></a>\_diffrn\_refln\_counts\_net

The diffractometer counts for the measurements: background
 before the peak, background after the peak, net counts after
 background removed, counts for peak scan or position, and the
 total counts (background plus peak).

### <a name="_diffrn_refln_counts_peak"></a>\_diffrn\_refln\_counts\_peak

The diffractometer counts for the measurements: background
 before the peak, background after the peak, net counts after
 background removed, counts for peak scan or position, and the
 total counts (background plus peak).

### <a name="_diffrn_refln_counts_total"></a>\_diffrn\_refln\_counts\_total

The diffractometer counts for the measurements: background
 before the peak, background after the peak, net counts after
 background removed, counts for peak scan or position, and the
 total counts (background plus peak).

### <a name="_diffrn_refln_crystal_id"></a>\_diffrn\_refln\_crystal\_id

Code identifying each crystal if multiple crystals are used. Is
 used to link with [\_exptl\_crystal\_id](#_exptl_crystal_id) in the [\_exptl\_crystal](#_exptl_crystal)\_ list.

### <a name="_diffrn_refln_detect_slit_horiz"></a>\_diffrn\_refln\_detect\_slit\_horiz

Total slit apertures in degrees in the diffraction plane
 (\*\_horiz) and perpendicular to the diffraction plane (\*\_vert).

Units: degrees

### <a name="_diffrn_refln_detect_slit_vert"></a>\_diffrn\_refln\_detect\_slit\_vert

Total slit apertures in degrees in the diffraction plane
 (\*\_horiz) and perpendicular to the diffraction plane (\*\_vert).

Units: degrees

### <a name="_diffrn_refln_elapsed_time"></a>\_diffrn\_refln\_elapsed\_time

Elapsed time in minutes from the start of the diffraction
 experiment to the measurement of this intensity.

Units: minutes

### <a name="_diffrn_refln_index_h"></a>\_diffrn\_refln\_index\_h

Miller indices of a measured reflection. These need not match
 the [\_refln\_index\_h](#_refln_index_h), \*\_k, \*\_l values if a transformation of the
 original measured cell has taken place. Details of the cell
 transformation are given in [\_diffrn\_reflns\_reduction\_process](#_diffrn_reflns_reduction_process).
 See also \_diffrn\_reflns\_transf\_matrix\_.

### <a name="_diffrn_refln_index_k"></a>\_diffrn\_refln\_index\_k

Miller indices of a measured reflection. These need not match
 the [\_refln\_index\_h](#_refln_index_h), \*\_k, \*\_l values if a transformation of the
 original measured cell has taken place. Details of the cell
 transformation are given in [\_diffrn\_reflns\_reduction\_process](#_diffrn_reflns_reduction_process).
 See also \_diffrn\_reflns\_transf\_matrix\_.

### <a name="_diffrn_refln_index_l"></a>\_diffrn\_refln\_index\_l

Miller indices of a measured reflection. These need not match
 the [\_refln\_index\_h](#_refln_index_h), \*\_k, \*\_l values if a transformation of the
 original measured cell has taken place. Details of the cell
 transformation are given in [\_diffrn\_reflns\_reduction\_process](#_diffrn_reflns_reduction_process).
 See also \_diffrn\_reflns\_transf\_matrix\_.

### <a name="_diffrn_refln_intensity_net"></a>\_diffrn\_refln\_intensity\_net

Net intensity calculated from the diffraction counts after
 the attenuator and standard scales have been applied.

### <a name="_diffrn_refln_intensity_sigma"></a>\_diffrn\_refln\_intensity\_sigma

Standard uncertainty (e.s.d.) of the net intensity calculated
 from the diffraction counts after the attenuator and standard
 scales have been applied.

### <a name="_diffrn_refln_intensity_u"></a>\_diffrn\_refln\_intensity\_u

Standard uncertainty of the net intensity calculated from
 the diffraction counts after the attenuator and standard
 scales have been applied.

### <a name="_diffrn_refln_scale_group_code"></a>\_diffrn\_refln\_scale\_group\_code

The code identifying the scale applicable to this reflection.
 This code must match with a specified [\_diffrn\_scale\_group\_code](#_diffrn_scale_group_code)
 value.

### <a name="_diffrn_refln_scan_mode"></a>\_diffrn\_refln\_scan\_mode

The code identifying the mode of scanning for measurements
 using a diffractometer. See [\_diffrn\_refln\_scan\_width](#_diffrn_refln_scan_width) and
 [\_diffrn\_refln\_scan\_mode\_backgd](#_diffrn_refln_scan_mode_backgd).

Values:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>om</td><td>omega scan</td></tr>
  <tr><td>ot</td><td>omega/2theta scan</td></tr>
  <tr><td>q</td><td>Q scans (arbitrary reciprocal directions)</td></tr>
</table>
### <a name="_diffrn_refln_scan_mode_backgd"></a>\_diffrn\_refln\_scan\_mode\_backgd

The code identifying the mode of scanning a reflection to measure
 the background intensity.

Values:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>st</td><td>stationary counter background</td></tr>
  <tr><td>mo</td><td>moving counter background</td></tr>
</table>
### <a name="_diffrn_refln_scan_rate"></a>\_diffrn\_refln\_scan\_rate

The rate of scanning a reflection in
 degrees per minute to measure the intensity.

Units: degrees\_per\_minute

### <a name="_diffrn_refln_scan_time_backgd"></a>\_diffrn\_refln\_scan\_time\_backgd

The time spent measuring each background in seconds.

Units: seconds

### <a name="_diffrn_refln_scan_width"></a>\_diffrn\_refln\_scan\_width

The scan width in degrees of the scan mode defined by the code
 [\_diffrn\_refln\_scan\_mode](#_diffrn_refln_scan_mode).

Units: degrees

### <a name="_diffrn_refln_sint/lambda"></a>\_diffrn\_refln\_sint/lambda

The (sin theta)/lambda value in reciprocal angstroms for
 this reflection.

Units: reciprocal\_angstroms

### <a name="_diffrn_refln_standard_code"></a>\_diffrn\_refln\_standard\_code

A code indicating that this reflection was measured as a
 standard reflection. The value must be &#39;.&#39; or match one of
 the [\_diffrn\_standard\_refln\_code](#_diffrn_standard_refln_code) values.

### <a name="_diffrn_refln_wavelength"></a>\_diffrn\_refln\_wavelength

The mean wavelength in angstroms of the radiation used to measure
 the intensity of this reflection. This is an important parameter
 for reflections measured using energy-dispersive detectors or the
 Laue method.

Units: angstroms

### <a name="_diffrn_refln_wavelength_id"></a>\_diffrn\_refln\_wavelength\_id

Code identifying the wavelength in the [\_diffrn\_radiation](#_diffrn_radiation)\_ list.

## <a name="DIFFRN_REFLNS"></a>DIFFRN\_REFLNS

Data items in the DIFFRN\_REFLNS category record details about
 the set of intensities measured in the diffraction experiment.

 The DIFFRN\_REFLNS data items specify the parameters that apply
 to all intensity measurements. The DIFFRN\_REFLNS data items
 are not looped.

 (The DIFFRN\_REFLN data items refer to individual intensity
 measurements and must be included in looped lists.)

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
_diffrn_reflns_number              1592
_diffrn_reflns_av_R_equivalents    0
_diffrn_reflns_av_unetI/netI       .027
_diffrn_reflns_limit_h_min         0
_diffrn_reflns_limit_h_max         6
_diffrn_reflns_limit_k_min        -17
_diffrn_reflns_limit_k_max         0
_diffrn_reflns_limit_l_min         0
_diffrn_reflns_limit_l_max         22
_diffrn_reflns_theta_min           3.71
_diffrn_reflns_theta_max           61.97
</code></pre>
  </td><td>Example 1 - based on data set TOZ of Willis, Beckwith &amp; Tozer
        [Acta Cryst. (1991), C47, 2276-2277].
  </td></tr>
</table>
### <a name="_diffrn_reflns_av_R_equivalents"></a>\_diffrn\_reflns\_av\_R\_equivalents

The residual [sum av|del(I)| / sum |av(I)|] for
 symmetry-equivalent reflections used to calculate the
 average intensity av(I). The av|del(I)| term is the
 average absolute difference between av(I) and the
 individual symmetry-equivalent intensities.

### <a name="_diffrn_reflns_av_sigmaI/netI"></a>\_diffrn\_reflns\_av\_sigmaI/netI

Measure [sum |u(net I)|/sum|net I|] for all measured reflections.

### <a name="_diffrn_reflns_av_unetI/netI"></a>\_diffrn\_reflns\_av\_unetI/netI

Measure [sum |u(net I)|/sum|net I|] for all measured reflections.

### <a name="_diffrn_reflns_Laue_measured_fraction_full"></a>\_diffrn\_reflns\_Laue\_measured\_fraction\_full

Fraction of Laue unique reflections (symmetry-independent in
 the Laue group) measured out to the resolution given in
 [\_diffrn\_reflns\_resolution\_full](#_diffrn_reflns_resolution_full) or [\_diffrn\_reflns\_theta\_full](#_diffrn_reflns_theta_full).
 The Laue group always contains a centre of symmetry so that
 the reflection h,k,l is always equivalent to the reflection
 -h,-k,-l even in space groups without a centre of symmetry.
 This number should not be less than 0.95, since it represents
 the fraction of reflections measured in the part of the
 diffraction pattern that is essentially complete.

### <a name="_diffrn_reflns_Laue_measured_fraction_max"></a>\_diffrn\_reflns\_Laue\_measured\_fraction\_max

Fraction of Laue unique reflections (symmetry-independent in
 the Laue group) measured out to the resolution given in
 [\_diffrn\_reflns\_resolution\_max](#_diffrn_reflns_resolution_max) or [\_diffrn\_reflns\_theta\_max](#_diffrn_reflns_theta_max).
 The Laue group always contains a centre of symmetry so that the
 reflection h,k,l is always equivalent to the reflection -h,-k,-l
 even in space groups without a centre of symmetry.

### <a name="_diffrn_reflns_limit_h_max"></a>\_diffrn\_reflns\_limit\_h\_max

The limits on the Miller indices of the intensities specified
 by [\_diffrn\_refln\_index\_h](#_diffrn_refln_index_h), \*\_k, \*\_l.

### <a name="_diffrn_reflns_limit_h_min"></a>\_diffrn\_reflns\_limit\_h\_min

The limits on the Miller indices of the intensities specified
 by [\_diffrn\_refln\_index\_h](#_diffrn_refln_index_h), \*\_k, \*\_l.

### <a name="_diffrn_reflns_limit_k_max"></a>\_diffrn\_reflns\_limit\_k\_max

The limits on the Miller indices of the intensities specified
 by [\_diffrn\_refln\_index\_h](#_diffrn_refln_index_h), \*\_k, \*\_l.

### <a name="_diffrn_reflns_limit_k_min"></a>\_diffrn\_reflns\_limit\_k\_min

The limits on the Miller indices of the intensities specified
 by [\_diffrn\_refln\_index\_h](#_diffrn_refln_index_h), \*\_k, \*\_l.

### <a name="_diffrn_reflns_limit_l_max"></a>\_diffrn\_reflns\_limit\_l\_max

The limits on the Miller indices of the intensities specified
 by [\_diffrn\_refln\_index\_h](#_diffrn_refln_index_h), \*\_k, \*\_l.

### <a name="_diffrn_reflns_limit_l_min"></a>\_diffrn\_reflns\_limit\_l\_min

The limits on the Miller indices of the intensities specified
 by [\_diffrn\_refln\_index\_h](#_diffrn_refln_index_h), \*\_k, \*\_l.

### <a name="_diffrn_reflns_number"></a>\_diffrn\_reflns\_number

The total number of measured intensities, excluding
 reflections that are classed as systematically absent arising
 from translational symmetry in the crystal unit cell.

### <a name="_diffrn_reflns_point_group_measured_fraction_full"></a>\_diffrn\_reflns\_point\_group\_measured\_fraction\_full

Fraction of crystal point-group unique reflections (i.e.
 symmetry-independent in the crystal point group) measured
 out to the resolution given in [\_diffrn\_reflns\_resolution\_full](#_diffrn_reflns_resolution_full)
 or [\_diffrn\_reflns\_theta\_full](#_diffrn_reflns_theta_full). For space groups that do not
 contain a centre of symmetry the reflections h,k,l and
 -h,-k,-l are independent. This number should not be less
 than 0.95, since it represents the fraction of reflections
 measured in the part of the diffraction pattern that is
 essentially complete.

### <a name="_diffrn_reflns_point_group_measured_fraction_max"></a>\_diffrn\_reflns\_point\_group\_measured\_fraction\_max

Fraction of crystal point-group unique reflections (i.e.
 symmetry-independent in the crystal point group) measured
 out to the resolution given in [\_diffrn\_reflns\_resolution\_max](#_diffrn_reflns_resolution_max)
 or [\_diffrn\_reflns\_theta\_max](#_diffrn_reflns_theta_max). For space groups that do not
 contain a centre of symmetry the reflections h,k,l and
 -h,-k,-l are independent.

### <a name="_diffrn_reflns_reduction_process"></a>\_diffrn\_reflns\_reduction\_process

A description of the process used to reduce the intensities
 into structure-factor magnitudes.

### <a name="_diffrn_reflns_resolution_full"></a>\_diffrn\_reflns\_resolution\_full

The resolution in reciprocal angstroms at which the measured
 reflection count is close to complete. The fraction of unique
 reflections measured out to this angle is given by
 [\_diffrn\_measured\_fraction\_theta\_full](#_diffrn_measured_fraction_theta_full).

Units: reciprocal\_angstroms

### <a name="_diffrn_reflns_resolution_max"></a>\_diffrn\_reflns\_resolution\_max

Maximum resolution in reciprocal angstroms of the measured
 diffraction pattern. The fraction of unique reflections
 measured out to this angle is given by
 [\_diffrn\_measured\_fraction\_theta\_max](#_diffrn_measured_fraction_theta_max)

Units: reciprocal\_angstroms

### <a name="_diffrn_reflns_theta_full"></a>\_diffrn\_reflns\_theta\_full

The theta angle (in degrees) at which the measured reflection
 count is close to complete. The fraction of unique reflections
 measured out to this angle is given by
 [\_diffrn\_measured\_fraction\_theta\_full](#_diffrn_measured_fraction_theta_full).

Units: degrees

### <a name="_diffrn_reflns_theta_max"></a>\_diffrn\_reflns\_theta\_max

Maximum theta angle in degrees for the measured intensities.
 The fraction of unique reflections measured out to this angle
 is given by [\_diffrn\_measured\_fraction\_theta\_max](#_diffrn_measured_fraction_theta_max)

Units: degrees

### <a name="_diffrn_reflns_theta_min"></a>\_diffrn\_reflns\_theta\_min

Minimum theta angle in degrees for the measured intensities.

Units: degrees

### <a name="_diffrn_reflns_transf_matrix_11"></a>\_diffrn\_reflns\_transf\_matrix\_11

Elements of the matrix used to transform the diffraction
 reflection indices [\_diffrn\_refln\_index\_h](#_diffrn_refln_index_h), \*\_k, \*\_l into the
 [\_refln\_index\_h](#_refln_index_h), \*\_k, \*\_l indices.
                            |11 12 13|
       (h k l) diffraction  |21 22 23|  =  (h&#39; k&#39; l&#39;)
                            |31 32 33|

### <a name="_diffrn_reflns_transf_matrix_12"></a>\_diffrn\_reflns\_transf\_matrix\_12

Elements of the matrix used to transform the diffraction
 reflection indices [\_diffrn\_refln\_index\_h](#_diffrn_refln_index_h), \*\_k, \*\_l into the
 [\_refln\_index\_h](#_refln_index_h), \*\_k, \*\_l indices.
                            |11 12 13|
       (h k l) diffraction  |21 22 23|  =  (h&#39; k&#39; l&#39;)
                            |31 32 33|

### <a name="_diffrn_reflns_transf_matrix_13"></a>\_diffrn\_reflns\_transf\_matrix\_13

Elements of the matrix used to transform the diffraction
 reflection indices [\_diffrn\_refln\_index\_h](#_diffrn_refln_index_h), \*\_k, \*\_l into the
 [\_refln\_index\_h](#_refln_index_h), \*\_k, \*\_l indices.
                            |11 12 13|
       (h k l) diffraction  |21 22 23|  =  (h&#39; k&#39; l&#39;)
                            |31 32 33|

### <a name="_diffrn_reflns_transf_matrix_21"></a>\_diffrn\_reflns\_transf\_matrix\_21

Elements of the matrix used to transform the diffraction
 reflection indices [\_diffrn\_refln\_index\_h](#_diffrn_refln_index_h), \*\_k, \*\_l into the
 [\_refln\_index\_h](#_refln_index_h), \*\_k, \*\_l indices.
                            |11 12 13|
       (h k l) diffraction  |21 22 23|  =  (h&#39; k&#39; l&#39;)
                            |31 32 33|

### <a name="_diffrn_reflns_transf_matrix_22"></a>\_diffrn\_reflns\_transf\_matrix\_22

Elements of the matrix used to transform the diffraction
 reflection indices [\_diffrn\_refln\_index\_h](#_diffrn_refln_index_h), \*\_k, \*\_l into the
 [\_refln\_index\_h](#_refln_index_h), \*\_k, \*\_l indices.
                            |11 12 13|
       (h k l) diffraction  |21 22 23|  =  (h&#39; k&#39; l&#39;)
                            |31 32 33|

### <a name="_diffrn_reflns_transf_matrix_23"></a>\_diffrn\_reflns\_transf\_matrix\_23

Elements of the matrix used to transform the diffraction
 reflection indices [\_diffrn\_refln\_index\_h](#_diffrn_refln_index_h), \*\_k, \*\_l into the
 [\_refln\_index\_h](#_refln_index_h), \*\_k, \*\_l indices.
                            |11 12 13|
       (h k l) diffraction  |21 22 23|  =  (h&#39; k&#39; l&#39;)
                            |31 32 33|

### <a name="_diffrn_reflns_transf_matrix_31"></a>\_diffrn\_reflns\_transf\_matrix\_31

Elements of the matrix used to transform the diffraction
 reflection indices [\_diffrn\_refln\_index\_h](#_diffrn_refln_index_h), \*\_k, \*\_l into the
 [\_refln\_index\_h](#_refln_index_h), \*\_k, \*\_l indices.
                            |11 12 13|
       (h k l) diffraction  |21 22 23|  =  (h&#39; k&#39; l&#39;)
                            |31 32 33|

### <a name="_diffrn_reflns_transf_matrix_32"></a>\_diffrn\_reflns\_transf\_matrix\_32

Elements of the matrix used to transform the diffraction
 reflection indices [\_diffrn\_refln\_index\_h](#_diffrn_refln_index_h), \*\_k, \*\_l into the
 [\_refln\_index\_h](#_refln_index_h), \*\_k, \*\_l indices.
                            |11 12 13|
       (h k l) diffraction  |21 22 23|  =  (h&#39; k&#39; l&#39;)
                            |31 32 33|

### <a name="_diffrn_reflns_transf_matrix_33"></a>\_diffrn\_reflns\_transf\_matrix\_33

Elements of the matrix used to transform the diffraction
 reflection indices [\_diffrn\_refln\_index\_h](#_diffrn_refln_index_h), \*\_k, \*\_l into the
 [\_refln\_index\_h](#_refln_index_h), \*\_k, \*\_l indices.
                            |11 12 13|
       (h k l) diffraction  |21 22 23|  =  (h&#39; k&#39; l&#39;)
                            |31 32 33|

## <a name="DIFFRN_REFLNS_CLASS"></a>DIFFRN\_REFLNS\_CLASS

Data items in the DIFFRN\_REFLNS\_CLASS category record details
 about the classes of reflections measured in the diffraction
 experiment.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
    _diffrn_reflns_class_number
    _diffrn_reflns_class_d_res_high
    _diffrn_reflns_class_d_res_low
    _diffrn_reflns_class_av_R_eq
    _diffrn_reflns_class_code
    _diffrn_reflns_class_description
        1580 0.551 6.136 0.015 &#39;Main&#39;
                                &#39;m=0; main reflections&#39;
        1045 0.551 6.136 0.010
                   &#39;Sat1&#39; &#39;m=1; first-order satellites&#39;
</code></pre>
  </td><td>Example 1 - example corresponding to the one-dimensional incommensurately
            modulated structure of K~2~SeO~4~. Each reflection class is
            defined by the number m=sum|m~i~|, where the m~i~ are the
            integer coefficients that, in addition to h,k,l, index the
            corresponding diffraction vector in the basis defined for
            the reciprocal lattice.
  </td></tr>
</table>
### <a name="_diffrn_reflns_class_av_R_eq"></a>\_diffrn\_reflns\_class\_av\_R\_eq

For each reflection class, the residual
 [sum av|del(I)|/sum|av(I)|] for symmetry-equivalent reflections
 used to calculate the average intensity av(I). The av|del(I)|
 term is the average absolute difference between av(I) and the
 individual intensities.

### <a name="_diffrn_reflns_class_av_sgI/I"></a>\_diffrn\_reflns\_class\_av\_sgI/I

Measure [sum|u(net I)|/sum|net I|] for all measured intensities
 in a reflection class.

### <a name="_diffrn_reflns_class_av_uI/I"></a>\_diffrn\_reflns\_class\_av\_uI/I

Measure [sum|u(net I)|/sum|net I|] for all measured intensities
 in a reflection class.

### <a name="_diffrn_reflns_class_code"></a>\_diffrn\_reflns\_class\_code

The code identifying a certain reflection class.

### <a name="_diffrn_reflns_class_d_res_high"></a>\_diffrn\_reflns\_class\_d\_res\_high

The smallest value in angstroms of the interplanar
 spacings of the reflections in each reflection class.
 This is called the highest resolution for this reflection class.

Units: angstroms

### <a name="_diffrn_reflns_class_d_res_low"></a>\_diffrn\_reflns\_class\_d\_res\_low

The highest value in angstroms of the interplanar
 spacings of the reflections in each reflection class.
 This is called the lowest resolution for this reflection class.

Units: angstroms

### <a name="_diffrn_reflns_class_description"></a>\_diffrn\_reflns\_class\_description

Description of each reflection class.

### <a name="_diffrn_reflns_class_number"></a>\_diffrn\_reflns\_class\_number

The total number of measured intensities for each reflection
 class, excluding the systematic absences arising from
 centring translations.

## <a name="DIFFRN_SCALE_GROUP"></a>DIFFRN\_SCALE\_GROUP

Data items in the DIFFRN\_SCALE\_GROUP category record details
 of the scaling factors applied to place all intensities in
 the reflection lists on a common scale.

 Scaling groups might, for instance, correspond to each film
 in a multi-film data set or each crystal in a multi-crystal
 data set.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
_diffrn_scale_group_code
_diffrn_scale_group_I_net
  1    .86473
  2   1.0654
</code></pre>
  </td><td>Example 1 - hypothetical example.
  </td></tr>
</table>
### <a name="_diffrn_scale_group_code"></a>\_diffrn\_scale\_group\_code

The code identifying a specific measurement group (e.g. for
 multi-film or multi-crystal data). The code must match a
 [\_diffrn\_refln\_scale\_group\_code](#_diffrn_refln_scale_group_code) in the reflection list.

### <a name="_diffrn_scale_group_I_net"></a>\_diffrn\_scale\_group\_I\_net

The scale for a specific measurement group which is to be
 multiplied with the net intensity to place all intensities
 in the [\_diffrn\_refln](#_diffrn_refln)\_ or [\_refln](#_refln)\_ list on a common scale.

## <a name="DIFFRN_SOURCE"></a>DIFFRN\_SOURCE

Data items in the DIFFRN\_SOURCE category record details of
 the source of radiation used in the diffraction experiment.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
_diffrn_source               &#39;rotating anode X-ray tube&#39;
_diffrn_source_type          &#39;Rigaku RU-200&#39;
_diffrn_source_power         50
_diffrn_source_current       180
_diffrn_source_size          &#39;8 mm x 0.4 mm broad focus&#39;
</code></pre>
  </td><td>Example 1 - based on PDB entry 5HVP and laboratory records for the
            structure corresponding to PDB entry 5HVP.
  </td></tr>
</table>
### <a name="_diffrn_radiation_source"></a>\_diffrn\_radiation\_source

The source of radiation.

### <a name="_diffrn_source"></a>\_diffrn\_source

The general class of the source of radiation.

### <a name="_diffrn_source_current"></a>\_diffrn\_source\_current

The current in milliamperes at which the radiation source was
 operated.

Units: milliamperes

### <a name="_diffrn_source_details"></a>\_diffrn\_source\_details

A description of special aspects of the source.

### <a name="_diffrn_source_power"></a>\_diffrn\_source\_power

The power in kilowatts at which the radiation source was
 operated.

Units: kilowatts

### <a name="_diffrn_source_size"></a>\_diffrn\_source\_size

The dimensions of the source as viewed from the sample.

### <a name="_diffrn_source_take-off_angle"></a>\_diffrn\_source\_take-off\_angle

The complement of the angle in degrees between the normal
 to the surface of the X-ray tube target and the primary
 X-ray beam for beams generated by traditional X-ray tubes.

### <a name="_diffrn_source_target"></a>\_diffrn\_source\_target

The chemical element symbol for the X-ray target
 (usually the anode) used to generate X-rays.
 This can also be used for spallation sources.

Values:

* H
* He
* Li
* Be
* B
* C
* N
* O
* F
* Ne
* Na
* Mg
* Al
* Si
* P
* S
* Cl
* Ar
* K
* Ca
* Sc
* Ti
* V
* Cr
* Mn
* Fe
* Co
* Ni
* Cu
* Zn
* Ga
* Ge
* As
* Se
* Br
* Kr
* Rb
* Sr
* Y
* Zr
* Nb
* Mo
* Tc
* Ru
* Rh
* Pd
* Ag
* Cd
* In
* Sn
* Sb
* Te
* I
* Xe
* Cs
* Ba
* La
* Ce
* Pr
* Nd
* Pm
* Sm
* Eu
* Gd
* Tb
* Dy
* Ho
* Er
* Tm
* Yb
* Lu
* Hf
* Ta
* W
* Re
* Os
* Ir
* Pt
* Au
* Hg
* Tl
* Pb
* Bi
* Po
* At
* Rn
* Fr
* Ra
* Ac
* Th
* Pa
* U
* Np
* Pu
* Am
* Cm
* Bk
* Cf
* Es
* Fm
* Md
* No
* Lr

### <a name="_diffrn_source_type"></a>\_diffrn\_source\_type

The make, model or name of the source of radiation.

### <a name="_diffrn_source_voltage"></a>\_diffrn\_source\_voltage

The voltage in kilovolts at which the radiation source was
 operated.

Units: kilovolts

## <a name="DIFFRN_STANDARD_REFLN"></a>DIFFRN\_STANDARD\_REFLN

Data items in the DIFFRN\_STANDARD\_REFLN category record details
 about the reflections treated as standards during the measurement
 of the diffraction intensities.

 Note that these are the individual standard reflections, not the
 results of the analysis of the standard reflections.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
_diffrn_standard_refln_index_h
_diffrn_standard_refln_index_k
_diffrn_standard_refln_index_l
3 2 4    1 9 1    3 0 10
</code></pre>
  </td><td>Example 1 - based on data set TOZ of Willis, Beckwith &amp; Tozer
            [Acta Cryst. (1991), C47, 2276-2277].
  </td></tr>
</table>
### <a name="_diffrn_standard_refln_code"></a>\_diffrn\_standard\_refln\_code

The code identifying a reflection measured as a standard
 reflection with the indices \_diffrn\_standard\_refln\_index\_.
 This is the same code as the  [\_diffrn\_refln\_standard\_code](#_diffrn_refln_standard_code) in
 the [\_diffrn\_refln](#_diffrn_refln)\_ list.

### <a name="_diffrn_standard_refln_index_h"></a>\_diffrn\_standard\_refln\_index\_h

Miller indices of standard reflections used in the diffraction
 measurement process.

### <a name="_diffrn_standard_refln_index_k"></a>\_diffrn\_standard\_refln\_index\_k

Miller indices of standard reflections used in the diffraction
 measurement process.

### <a name="_diffrn_standard_refln_index_l"></a>\_diffrn\_standard\_refln\_index\_l

Miller indices of standard reflections used in the diffraction
 measurement process.

## <a name="DIFFRN_STANDARDS"></a>DIFFRN\_STANDARDS

Data items in the DIFFRN\_STANDARDS category record details
 about the set of standard reflections used to monitor intensity
 stability during the measurement of diffraction intensities.

 Note that these records describe properties common to the set of
 standard reflections, not the standard reflections themselves.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
_diffrn_standards_number            3
_diffrn_standards_interval_time     120
_diffrn_standards_decay_%           0
</code></pre>
  </td><td>Example 1 - based on data set TOZ of Willis, Beckwith &amp; Tozer
           [Acta Cryst. (1991), C47, 2276-2277].
  </td></tr>
</table>
### <a name="_diffrn_standards_decay_%"></a>\_diffrn\_standards\_decay\_%

The percentage decrease in the mean
 intensity of the set of standard reflections measured at the
 start of the measurement process and at the finish.  This value
 usually affords a measure of the overall decay in crystal
 quality during the diffraction measurement process.  Negative
 values are used in exceptional instances where the final
 intensities are greater than the initial ones.  If no
 measurable decay has occurred, the standard uncertainty should
 be quoted to indicate the maximum possible value the decay
 might have.  A range of 3 standard uncertainties is considered
 possible.  Thus 0.0(1) would indicate a decay of less than
 0.3% or an enhancement of less than 0.3%.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
0.5(1)
  </td><td>represents a decay between 0.2% and 0.8%
  </td></tr>
  <tr><td>
-1(1)
  </td><td>the change in the standards lies between
 a decay of 2% and an increase of 4%
  </td></tr>
  <tr><td>
0.0(2)
  </td><td>the change in the standards lies between a
 decay of 0.6% and an increase of 0.6%.
  </td></tr>
</table>
### <a name="_diffrn_standards_interval_count"></a>\_diffrn\_standards\_interval\_count

The number of reflection intensities, or the time in minutes,
 between the measurement of standard reflection intensities.

### <a name="_diffrn_standards_interval_time"></a>\_diffrn\_standards\_interval\_time

The number of reflection intensities, or the time in minutes,
 between the measurement of standard reflection intensities.

### <a name="_diffrn_standards_number"></a>\_diffrn\_standards\_number

The number of unique standard reflections used during the
 measurement of the diffraction intensities.

### <a name="_diffrn_standards_scale_sigma"></a>\_diffrn\_standards\_scale\_sigma

The standard uncertainty (e.s.d.) of the individual mean
 standard scales applied to the intensity data.

### <a name="_diffrn_standards_scale_u"></a>\_diffrn\_standards\_scale\_u

The standard uncertainty of the individual mean
 standard scales applied to the intensity data.

## <a name="EXPTL"></a>EXPTL

Data items in the EXPTL category record details about the
 experimental work prior to the intensity measurements and
 details about the absorption-correction technique employed.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
_exptl_absorpt_coefficient_mu     0.962
_exptl_absorpt_correction_type    psi-scan
_exptl_absorpt_process_details
                           &#39;North, Phillips &amp; Mathews (1968)&#39;
_exptl_absorpt_correction_T_min   0.929
_exptl_absorpt_correction_T_max   0.997
</code></pre>
  </td><td>Example 1 - based on a paper by Steiner [Acta Cryst. (1996), C52,
            2554-2556].
  </td></tr>
</table>
### <a name="_exptl_absorpt_coefficient_mu"></a>\_exptl\_absorpt\_coefficient\_mu

The absorption coefficient mu in reciprocal millimetres
 calculated from the atomic content of the cell, the density and
 the radiation wavelength.

Units: reciprocal\_millimetres

### <a name="_exptl_absorpt_correction_T_max"></a>\_exptl\_absorpt\_correction\_T\_max

The maximum and minimum transmission factors applied to the
 diffraction pattern measured in this experiment. These
 factors are also referred to as the absorption correction
 A or 1/A\*. As this value is the one that is applied to
 the measured intensities, it includes the correction for
 absorption by the specimen mount and diffractometer as well
 as by the specimen itself.

### <a name="_exptl_absorpt_correction_T_min"></a>\_exptl\_absorpt\_correction\_T\_min

The maximum and minimum transmission factors applied to the
 diffraction pattern measured in this experiment. These
 factors are also referred to as the absorption correction
 A or 1/A\*. As this value is the one that is applied to
 the measured intensities, it includes the correction for
 absorption by the specimen mount and diffractometer as well
 as by the specimen itself.

### <a name="_exptl_absorpt_correction_type"></a>\_exptl\_absorpt\_correction\_type

The absorption-correction type and method. The value &#39;empirical&#39;
 should NOT be used unless more detailed information is not
 available.

Values:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>analytical</td><td>analytical from crystal shape</td></tr>
  <tr><td>cylinder</td><td>cylindrical</td></tr>
  <tr><td>empirical</td><td>empirical from intensities</td></tr>
  <tr><td>gaussian</td><td>Gaussian from crystal shape</td></tr>
  <tr><td>integration</td><td>integration from crystal shape</td></tr>
  <tr><td>multi-scan</td><td>symmetry-related measurements</td></tr>
  <tr><td>none</td><td>no absorption correction applied</td></tr>
  <tr><td>numerical</td><td>numerical from crystal shape</td></tr>
  <tr><td>psi-scan</td><td>psi-scan corrections</td></tr>
  <tr><td>refdelf</td><td>refined from delta-F</td></tr>
  <tr><td>sphere</td><td>spherical</td></tr>
</table>
### <a name="_exptl_absorpt_process_details"></a>\_exptl\_absorpt\_process\_details

Description of the absorption process applied to the
 intensities. A literature reference should be supplied
 for psi-scan techniques.

### <a name="_exptl_crystals_number"></a>\_exptl\_crystals\_number

The total number of crystals used for the measurement of
 intensities.

### <a name="_exptl_special_details"></a>\_exptl\_special\_details

Any special information about the experimental work prior to the
 intensity measurements. See also [\_exptl\_crystal\_preparation](#_exptl_crystal_preparation).

### <a name="_exptl_transmission_factor_max"></a>\_exptl\_transmission\_factor\_max

The calculated maximum value of the transmission factor for
 the specimen. Its value does not include the effects of
 absorption in the specimen mount. The presence of this
 item does not imply that the structure factors have been
 corrected for absorption. The applied correction should be 
 given by [\_exptl\_absorpt\_correction\_T\_max](#_exptl_absorpt_correction_T_max).

### <a name="_exptl_transmission_factor_min"></a>\_exptl\_transmission\_factor\_min

The calculated minimum value of the transmission factor for
 the specimen. Its value does not include the effects of
 absorption in the specimen mount. The presence of this
 item does not imply that the structure factors have been
 corrected for absorption. The applied correction should be 
 given by [\_exptl\_absorpt\_correction\_T\_min](#_exptl_absorpt_correction_T_min).

## <a name="EXPTL_CRYSTAL"></a>EXPTL\_CRYSTAL

Data items in the EXPTL\_CRYSTAL category record details about
 experimental measurements on the crystal or crystals used,
 such as shape, size or density.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
_exptl_crystal_description          prism
_exptl_crystal_colour               colourless
_exptl_crystal_size_max             0.32
_exptl_crystal_size_mid             0.27
_exptl_crystal_size_min             0.10
_exptl_crystal_density_diffrn       1.146
_exptl_crystal_density_meas         ?
_exptl_crystal_density_method       &#39;not measured&#39;
_exptl_crystal_F_000                656
</code></pre>
  </td><td>Example 1 - based on data set TOZ of Willis, Beckwith &amp; Tozer
            [Acta Cryst. (1991), C47, 2276-2277].
  </td></tr>
  <tr><td>
<pre><code>
_exptl_crystal_density_meas_gt       2.5
 _exptl_crystal_density_meas_lt       5.0
</code></pre>
  </td><td>Example 2 - using separate items to define upper and lower
            limits for a value.
  </td></tr>
  <tr><td>
_exptl_crystal_density_meas_temp_lt 300
  </td><td>Example 3 - here the density was measured at some
                unspecified temperature below room temperature.
  </td></tr>
</table>
### <a name="_exptl_crystal_colour"></a>\_exptl\_crystal\_colour

The colour of the crystal.

### <a name="_exptl_crystal_colour_lustre"></a>\_exptl\_crystal\_colour\_lustre

The enumeration list of standardized names developed for the
 International Centre for Diffraction Data.
 The colour of a crystal is given by the combination of
 [\_exptl\_crystal\_colour\_modifier](#_exptl_crystal_colour_modifier) with
 [\_exptl\_crystal\_colour\_primary](#_exptl_crystal_colour_primary), as in &#39;dark-green&#39; or
 &#39;bluish-violet&#39;, if necessary combined with
 [\_exptl\_crystal\_colour\_lustre](#_exptl_crystal_colour_lustre), as in &#39;metallic-green&#39;.

Values:

* metallic
* dull
* clear

### <a name="_exptl_crystal_colour_modifier"></a>\_exptl\_crystal\_colour\_modifier

The enumeration list of standardized names developed for the
 International Centre for Diffraction Data.
 The colour of a crystal is given by the combination of
 [\_exptl\_crystal\_colour\_modifier](#_exptl_crystal_colour_modifier) with
 [\_exptl\_crystal\_colour\_primary](#_exptl_crystal_colour_primary), as in &#39;dark-green&#39; or
 &#39;bluish-violet&#39;, if necessary combined with
 [\_exptl\_crystal\_colour\_lustre](#_exptl_crystal_colour_lustre), as in &#39;metallic-green&#39;.

Values:

* light
* dark
* whitish
* blackish
* grayish
* brownish
* reddish
* pinkish
* orangish
* yellowish
* greenish
* bluish

### <a name="_exptl_crystal_colour_primary"></a>\_exptl\_crystal\_colour\_primary

The enumeration list of standardized names developed for the
 International Centre for Diffraction Data.
 The colour of a crystal is given by the combination of
 [\_exptl\_crystal\_colour\_modifier](#_exptl_crystal_colour_modifier) with
 [\_exptl\_crystal\_colour\_primary](#_exptl_crystal_colour_primary), as in &#39;dark-green&#39; or
 &#39;bluish-violet&#39;, if necessary combined with
 [\_exptl\_crystal\_colour\_lustre](#_exptl_crystal_colour_lustre), as in &#39;metallic-green&#39;.

Values:

* colourless
* white
* black
* gray
* brown
* red
* pink
* orange
* yellow
* green
* blue
* violet

### <a name="_exptl_crystal_density_diffrn"></a>\_exptl\_crystal\_density\_diffrn

Density values calculated from the crystal cell and contents. The
 units are megagrams per cubic metre (grams per cubic centimetre).

Units: megagrams\_per\_cubic\_metre

### <a name="_exptl_crystal_density_meas"></a>\_exptl\_crystal\_density\_meas

Density values measured using standard chemical and physical
 methods. The units are megagrams per cubic metre (grams per
 cubic centimetre).

Units: megagrams\_per\_cubic\_metre

### <a name="_exptl_crystal_density_meas_gt"></a>\_exptl\_crystal\_density\_meas\_gt

The value above which the density measured using standard
 chemical and physical methods lies. The units are megagrams
 per cubic metre (grams per cubic centimetre).
 [\_exptl\_crystal\_density\_meas\_gt](#_exptl_crystal_density_meas_gt) and
 [\_exptl\_crystal\_density\_meas\_lt](#_exptl_crystal_density_meas_lt) should not be used to
 report new experimental work, for which
 [\_exptl\_crystal\_density\_meas](#_exptl_crystal_density_meas) should be used. These items
 are intended for use in reporting information in
 existing databases and archives which would be misleading if
 reported under [\_exptl\_crystal\_density\_meas](#_exptl_crystal_density_meas).

Units: megagrams\_per\_cubic\_metre

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
2.5
  </td><td>lower limit for the density (only the range
 within which the density lies was given in the
 original paper)
  </td></tr>
</table>
### <a name="_exptl_crystal_density_meas_lt"></a>\_exptl\_crystal\_density\_meas\_lt

The value below which the density measured using standard
 chemical and physical methods lies. The units are megagrams
 per cubic metre (grams per cubic centimetre).
 [\_exptl\_crystal\_density\_meas\_gt](#_exptl_crystal_density_meas_gt) and
 [\_exptl\_crystal\_density\_meas\_lt](#_exptl_crystal_density_meas_lt) should not be used to
 report new experimental work, for which
 [\_exptl\_crystal\_density\_meas](#_exptl_crystal_density_meas) should be used. These items
 are intended for use in reporting information in
 existing databases and archives which would be misleading if
 reported under [\_exptl\_crystal\_density\_meas](#_exptl_crystal_density_meas).

Units: megagrams\_per\_cubic\_metre

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
1.0
  </td><td>specimen floats in water
  </td></tr>
  <tr><td>
5.0
  </td><td>upper limit for the density (only the range
 within which the density lies was given in the
 original paper)
  </td></tr>
</table>
### <a name="_exptl_crystal_density_meas_temp"></a>\_exptl\_crystal\_density\_meas\_temp

Temperature in kelvins at which [\_exptl\_crystal\_density\_meas](#_exptl_crystal_density_meas)
 was determined.

Units: kelvin

### <a name="_exptl_crystal_density_meas_temp_gt"></a>\_exptl\_crystal\_density\_meas\_temp\_gt

Temperature in kelvins above which [\_exptl\_crystal\_density\_meas](#_exptl_crystal_density_meas)
 was determined. [\_exptl\_crystal\_density\_meas\_temp\_gt](#_exptl_crystal_density_meas_temp_gt) and
 [\_exptl\_crystal\_density\_meas\_temp\_lt](#_exptl_crystal_density_meas_temp_lt) should not be used for
 reporting new work, for which the correct temperature of
 measurement should be given. These items are intended for
 use in reporting information stored in databases
 or archives which would be misleading if reported under
 [\_exptl\_crystal\_density\_meas\_temp](#_exptl_crystal_density_meas_temp).

Units: kelvin

### <a name="_exptl_crystal_density_meas_temp_lt"></a>\_exptl\_crystal\_density\_meas\_temp\_lt

Temperature in kelvins below which [\_exptl\_crystal\_density\_meas](#_exptl_crystal_density_meas)
 was determined. [\_exptl\_crystal\_density\_meas\_temp\_gt](#_exptl_crystal_density_meas_temp_gt) and
 [\_exptl\_crystal\_density\_meas\_temp\_lt](#_exptl_crystal_density_meas_temp_lt) should not be used for
 reporting new work, for which the correct temperature of
 measurement should be given. These items are intended for
 use in reporting information stored in databases
 or archives which would be misleading if reported under
 [\_exptl\_crystal\_density\_meas\_temp](#_exptl_crystal_density_meas_temp).

Units: kelvin

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
300
  </td><td>The density was measured at some unspecified
 temperature below room temperature.
  </td></tr>
</table>
### <a name="_exptl_crystal_density_method"></a>\_exptl\_crystal\_density\_method

The method used to measure [\_exptl\_crystal\_density\_meas](#_exptl_crystal_density_meas).

### <a name="_exptl_crystal_description"></a>\_exptl\_crystal\_description

A description of the quality and habit of the crystal.
 The crystal dimensions should not normally be reported here;
 use instead \_exptl\_crystal\_size\_ for the gross dimensions of
 the crystal and [\_exptl\_crystal\_face](#_exptl_crystal_face)\_ to describe the
 relationship between individual faces.

### <a name="_exptl_crystal_F_000"></a>\_exptl\_crystal\_F\_000

The effective number of electrons in the crystal unit cell
 contributing to F(000). This may contain dispersion contributions
 and is calculated as

 F(000) = [ (sum f~r~)^2^ + (sum f~i~)^2^ ]^1/2^

 f~r~   = real part of the scattering factors at theta = 0
 f~i~   = imaginary part of the scattering factors at theta = 0

          the sum is taken over each atom in the unit cell

### <a name="_exptl_crystal_id"></a>\_exptl\_crystal\_id

Code identifying each crystal if multiple crystals are used. It
 is used to link with [\_diffrn\_refln\_crystal\_id](#_diffrn_refln_crystal_id) in the intensity
 measurements and with [\_refln\_crystal\_id](#_refln_crystal_id) in the [\_refln](#_refln)\_ list.

### <a name="_exptl_crystal_preparation"></a>\_exptl\_crystal\_preparation

Details of crystal growth and preparation of the crystal (e.g.
 mounting) prior to the intensity measurements.

### <a name="_exptl_crystal_pressure_history"></a>\_exptl\_crystal\_pressure\_history

Relevant details concerning the pressure history of the
 sample.

### <a name="_exptl_crystal_recrystallization_method"></a>\_exptl\_crystal\_recrystallization\_method

Describes the method used to recrystallize the sample.
 Sufficient details should be given for the procedure to be
 repeated.  The temperature or temperatures should be given as
 well as details of the solvent, flux or carrier gas with
 concentrations or pressures and ambient atmosphere.

### <a name="_exptl_crystal_size_length"></a>\_exptl\_crystal\_size\_length

The maximum, medial and minimum dimensions in millimetres of
 the crystal. If the crystal is a sphere, then the \*\_rad item is
 its radius. If the crystal is a cylinder, then the \*\_rad item
 is its radius and the \*\_length item is its length. These may
 appear in a list with [\_exptl\_crystal\_id](#_exptl_crystal_id) if multiple crystals
 are used in the experiment.

Units: millimetres

### <a name="_exptl_crystal_size_max"></a>\_exptl\_crystal\_size\_max

The maximum, medial and minimum dimensions in millimetres of
 the crystal. If the crystal is a sphere, then the \*\_rad item is
 its radius. If the crystal is a cylinder, then the \*\_rad item
 is its radius and the \*\_length item is its length. These may
 appear in a list with [\_exptl\_crystal\_id](#_exptl_crystal_id) if multiple crystals
 are used in the experiment.

Units: millimetres

### <a name="_exptl_crystal_size_mid"></a>\_exptl\_crystal\_size\_mid

The maximum, medial and minimum dimensions in millimetres of
 the crystal. If the crystal is a sphere, then the \*\_rad item is
 its radius. If the crystal is a cylinder, then the \*\_rad item
 is its radius and the \*\_length item is its length. These may
 appear in a list with [\_exptl\_crystal\_id](#_exptl_crystal_id) if multiple crystals
 are used in the experiment.

Units: millimetres

### <a name="_exptl_crystal_size_min"></a>\_exptl\_crystal\_size\_min

The maximum, medial and minimum dimensions in millimetres of
 the crystal. If the crystal is a sphere, then the \*\_rad item is
 its radius. If the crystal is a cylinder, then the \*\_rad item
 is its radius and the \*\_length item is its length. These may
 appear in a list with [\_exptl\_crystal\_id](#_exptl_crystal_id) if multiple crystals
 are used in the experiment.

Units: millimetres

### <a name="_exptl_crystal_size_rad"></a>\_exptl\_crystal\_size\_rad

The maximum, medial and minimum dimensions in millimetres of
 the crystal. If the crystal is a sphere, then the \*\_rad item is
 its radius. If the crystal is a cylinder, then the \*\_rad item
 is its radius and the \*\_length item is its length. These may
 appear in a list with [\_exptl\_crystal\_id](#_exptl_crystal_id) if multiple crystals
 are used in the experiment.

Units: millimetres

### <a name="_exptl_crystal_thermal_history"></a>\_exptl\_crystal\_thermal\_history

Relevant details concerning the thermal history of the
 sample.

## <a name="EXPTL_CRYSTAL_FACE"></a>EXPTL\_CRYSTAL\_FACE

Data items in the EXPTL\_CRYSTAL\_FACE category record details
 of the crystal faces.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
_exptl_crystal_face_index_h
_exptl_crystal_face_index_k
_exptl_crystal_face_index_l
_exptl_crystal_face_perp_dist
     0   -1   -2    .18274
     1    0   -2    .17571
    -1    1   -2    .17845
    -2    1    0    .21010
    -1    0    2    .18849
     1   -1    2    .20605
     2   -1    0    .24680
    -1    2    0    .19688
     0    1    2    .15206
</code></pre>
  </td><td>Example 1 - based on structure PAWD2 of Vittal &amp; Dean [Acta
            Cryst. (1996), C52, 1180-1182].
  </td></tr>
</table>
### <a name="_exptl_crystal_face_diffr_chi"></a>\_exptl\_crystal\_face\_diffr\_chi

The goniometer angle settings in degrees when the perpendicular
 to the specified crystal face is aligned along a specified
 direction (e.g. the bisector of the incident and reflected beams
 in an optical goniometer).


Units: degrees

### <a name="_exptl_crystal_face_diffr_kappa"></a>\_exptl\_crystal\_face\_diffr\_kappa

The goniometer angle settings in degrees when the perpendicular
 to the specified crystal face is aligned along a specified
 direction (e.g. the bisector of the incident and reflected beams
 in an optical goniometer).


Units: degrees

### <a name="_exptl_crystal_face_diffr_phi"></a>\_exptl\_crystal\_face\_diffr\_phi

The goniometer angle settings in degrees when the perpendicular
 to the specified crystal face is aligned along a specified
 direction (e.g. the bisector of the incident and reflected beams
 in an optical goniometer).


Units: degrees

### <a name="_exptl_crystal_face_diffr_psi"></a>\_exptl\_crystal\_face\_diffr\_psi

The goniometer angle settings in degrees when the perpendicular
 to the specified crystal face is aligned along a specified
 direction (e.g. the bisector of the incident and reflected beams
 in an optical goniometer).


Units: degrees

### <a name="_exptl_crystal_face_index_h"></a>\_exptl\_crystal\_face\_index\_h

Miller indices of the crystal face associated with the value
 [\_exptl\_crystal\_face\_perp\_dist](#_exptl_crystal_face_perp_dist).

### <a name="_exptl_crystal_face_index_k"></a>\_exptl\_crystal\_face\_index\_k

Miller indices of the crystal face associated with the value
 [\_exptl\_crystal\_face\_perp\_dist](#_exptl_crystal_face_perp_dist).

### <a name="_exptl_crystal_face_index_l"></a>\_exptl\_crystal\_face\_index\_l

Miller indices of the crystal face associated with the value
 [\_exptl\_crystal\_face\_perp\_dist](#_exptl_crystal_face_perp_dist).

### <a name="_exptl_crystal_face_perp_dist"></a>\_exptl\_crystal\_face\_perp\_dist

The perpendicular distance in millimetres from the face to the
 centre of rotation of the crystal.

Units: millimetres

## <a name="GEOM"></a>GEOM

Data items in the GEOM and related (GEOM\_ANGLE,
 GEOM\_BOND, GEOM\_CONTACT, GEOM\_HBOND and GEOM\_TORSION)
 categories record details about the molecular and crystal
 geometry as calculated from the ATOM,
 CELL and SYMMETRY data.

 Geometry data are usually redundant, in that they can be
 calculated from other more fundamental quantities in the data
 block. However, they serve the dual purposes of providing a
 check on the correctness of both sets of data and of enabling
 the most important geometric data to be identified for
 publication by setting the appropriate publication flag.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
_geom_special_details
    ;  All esds (except the esd in the dihedral angle between
       two l.s. planes) are estimated using the full covariance
       matrix. The cell esds are taken into account individually
       in the estimation of esds in distances, angles and
       torsion angles; correlations between esds in cell
       parameters are only used when they are defined by crystal
       symmetry. An approximate (isotropic) treatment of cell
       esds is used for estimating esds involving l.s. planes.
    ;
</code></pre>
  </td><td>Example 1 - based on data set bagan of Yamane &amp; DiSalvo [Acta
            Cryst. (1996), C52, 760-761].
  </td></tr>
</table>
### <a name="_geom_special_details"></a>\_geom\_special\_details

The description of geometrical information not covered by the
 existing data names in the geometry categories, such as
 least-squares planes.

## <a name="GEOM_ANGLE"></a>GEOM\_ANGLE

Data items in the GEOM\_ANGLE category record details about the
 bond angles as calculated from the ATOM,
 CELL and SYMMETRY data.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
_geom_angle_atom_site_label_1
_geom_angle_atom_site_label_2
_geom_angle_atom_site_label_3
_geom_angle
_geom_angle_site_symmetry_1
_geom_angle_site_symmetry_2
_geom_angle_site_symmetry_3
_geom_angle_publ_flag
 C2  O1  C5   111.6(2)  1_555  1_555  1_555  yes
 O1  C2  C3   110.9(2)  1_555  1_555  1_555  yes
 O1  C2  O21  122.2(3)  1_555  1_555  1_555  yes
 C3  C2  O21  127.0(3)  1_555  1_555  1_555  yes
 C2  C3  N4   101.3(2)  1_555  1_555  1_555  yes
 C2  C3  C31  111.3(2)  1_555  1_555  1_555  yes
 C2  C3  H3   107(1)    1_555  1_555  1_555  no
 N4  C3  C31  116.7(2)  1_555  1_555  1_555  yes
# - - - - data truncated for brevity - - - -
</code></pre>
  </td><td>Example 1 - based on data set TOZ of Willis, Beckwith &amp; Tozer
            [Acta Cryst. (1991), C47, 2276-2277].
  </td></tr>
</table>
### <a name="_geom_angle"></a>\_geom\_angle

Angle in degrees defined by the three sites
 \_geom\_angle\_atom\_site\_label\_1, \*\_2 and \*\_3. The site at \*\_2
 is at the apex of the angle.

Units: degrees

### <a name="_geom_angle_atom_site_label_1"></a>\_geom\_angle\_atom\_site\_label\_1

The labels of the three atom sites which define the angle
 given by [\_geom\_angle](#_geom_angle). These must match labels specified as
 [\_atom\_site\_label](#_atom_site_label) in the atom list. Label 2 identifies the site at
 the apex of the angle.

### <a name="_geom_angle_atom_site_label_2"></a>\_geom\_angle\_atom\_site\_label\_2

The labels of the three atom sites which define the angle
 given by [\_geom\_angle](#_geom_angle). These must match labels specified as
 [\_atom\_site\_label](#_atom_site_label) in the atom list. Label 2 identifies the site at
 the apex of the angle.

### <a name="_geom_angle_atom_site_label_3"></a>\_geom\_angle\_atom\_site\_label\_3

The labels of the three atom sites which define the angle
 given by [\_geom\_angle](#_geom_angle). These must match labels specified as
 [\_atom\_site\_label](#_atom_site_label) in the atom list. Label 2 identifies the site at
 the apex of the angle.

### <a name="_geom_angle_publ_flag"></a>\_geom\_angle\_publ\_flag

This code signals whether the angle is referred to in a
 publication or should be placed in a table of significant
 angles.

Values:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>no</td><td>do not include angle in special list</td></tr>
  <tr><td>n</td><td>abbreviation for &quot;no&quot;</td></tr>
  <tr><td>yes</td><td>do include angle in special list</td></tr>
  <tr><td>y</td><td>abbreviation for &quot;yes&quot;</td></tr>
</table>
Default value: 'no'

### <a name="_geom_angle_site_symmetry_1"></a>\_geom\_angle\_site\_symmetry\_1

The symmetry code of each atom site as the symmetry-equivalent
 position number &#39;n&#39; and the cell translation number &#39;klm&#39;.
 These numbers are combined to form the code &#39;n klm&#39; or n\_klm.
 The character string n\_klm is composed as follows:

 n refers to the symmetry operation that is applied to the
 coordinates stored in [\_atom\_site\_fract\_x](#_atom_site_fract_x), [\_atom\_site\_fract\_y](#_atom_site_fract_y)
 and [\_atom\_site\_fract\_z](#_atom_site_fract_z). It must match a number given in
 [\_space\_group\_symop\_id](#_space_group_symop_id).

 k, l and m refer to the translations that are subsequently
 applied to the symmetry-transformed coordinates to generate
 the atom used in calculating the angle. These translations
 (x,y,z) are related to (k,l,m) by the relations
      k = 5 + x
      l = 5 + y
      m = 5 + z
 By adding 5 to the translations, the use of negative numbers
 is avoided.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
.
  </td><td>no symmetry or translation to site
  </td></tr>
  <tr><td>
4
  </td><td>4th symmetry operation applied
  </td></tr>
  <tr><td>
7_645
  </td><td>7th symm. posn.; +a on x; -b on y
  </td></tr>
</table>
### <a name="_geom_angle_site_symmetry_2"></a>\_geom\_angle\_site\_symmetry\_2

The symmetry code of each atom site as the symmetry-equivalent
 position number &#39;n&#39; and the cell translation number &#39;klm&#39;.
 These numbers are combined to form the code &#39;n klm&#39; or n\_klm.
 The character string n\_klm is composed as follows:

 n refers to the symmetry operation that is applied to the
 coordinates stored in [\_atom\_site\_fract\_x](#_atom_site_fract_x), [\_atom\_site\_fract\_y](#_atom_site_fract_y)
 and [\_atom\_site\_fract\_z](#_atom_site_fract_z). It must match a number given in
 [\_space\_group\_symop\_id](#_space_group_symop_id).

 k, l and m refer to the translations that are subsequently
 applied to the symmetry-transformed coordinates to generate
 the atom used in calculating the angle. These translations
 (x,y,z) are related to (k,l,m) by the relations
      k = 5 + x
      l = 5 + y
      m = 5 + z
 By adding 5 to the translations, the use of negative numbers
 is avoided.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
.
  </td><td>no symmetry or translation to site
  </td></tr>
  <tr><td>
4
  </td><td>4th symmetry operation applied
  </td></tr>
  <tr><td>
7_645
  </td><td>7th symm. posn.; +a on x; -b on y
  </td></tr>
</table>
### <a name="_geom_angle_site_symmetry_3"></a>\_geom\_angle\_site\_symmetry\_3

The symmetry code of each atom site as the symmetry-equivalent
 position number &#39;n&#39; and the cell translation number &#39;klm&#39;.
 These numbers are combined to form the code &#39;n klm&#39; or n\_klm.
 The character string n\_klm is composed as follows:

 n refers to the symmetry operation that is applied to the
 coordinates stored in [\_atom\_site\_fract\_x](#_atom_site_fract_x), [\_atom\_site\_fract\_y](#_atom_site_fract_y)
 and [\_atom\_site\_fract\_z](#_atom_site_fract_z). It must match a number given in
 [\_space\_group\_symop\_id](#_space_group_symop_id).

 k, l and m refer to the translations that are subsequently
 applied to the symmetry-transformed coordinates to generate
 the atom used in calculating the angle. These translations
 (x,y,z) are related to (k,l,m) by the relations
      k = 5 + x
      l = 5 + y
      m = 5 + z
 By adding 5 to the translations, the use of negative numbers
 is avoided.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
.
  </td><td>no symmetry or translation to site
  </td></tr>
  <tr><td>
4
  </td><td>4th symmetry operation applied
  </td></tr>
  <tr><td>
7_645
  </td><td>7th symm. posn.; +a on x; -b on y
  </td></tr>
</table>
## <a name="GEOM_BOND"></a>GEOM\_BOND

Data items in the GEOM\_BOND category record details about
 bonds as calculated from the ATOM, CELL
 and SYMMETRY data.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
_geom_bond_atom_site_label_1
_geom_bond_atom_site_label_2
_geom_bond_distance
_geom_bond_site_symmetry_1
_geom_bond_site_symmetry_2
_geom_bond_publ_flag
  O1  C2   1.342(4)  1_555  1_555  yes
  O1  C5   1.439(3)  1_555  1_555  yes
  C2  C3   1.512(4)  1_555  1_555  yes
  C2  O21  1.199(4)  1_555  1_555  yes
  C3  N4   1.465(3)  1_555  1_555  yes
  C3  C31  1.537(4)  1_555  1_555  yes
  C3  H3   1.00(3)   1_555  1_555  no
  N4  C5   1.472(3)  1_555  1_555  yes
# - - - - data truncated for brevity - - - -
</code></pre>
  </td><td>Example 1 - based on data set TOZ of Willis, Beckwith &amp; Tozer
            [Acta Cryst. (1991), C47, 2276-2277].
  </td></tr>
  <tr><td>
<pre><code>
loop_
_geom_bond_atom_site_label_1
_geom_bond_atom_site_label_2
_geom_bond_distance
_geom_bond_multiplicity
Ca1   F1   2.495(9)    1
Ca1   F2   2.291(10)   2
Ca1   F2   2.391(11)   2
Ca1   F3   2.214(11)   2
Cr1   F1   1.940(11)   2
Cr1   F2   1.918(9)    2
Cr1   F3   1.848(10)   2
</code></pre>
  </td><td>Example 2 - An example showing a listing of only symmetry-unique bonds.
            In high-symmetry structures when many bonds are related by
            symmetry, it may not be necessary or desirable to list all
            the bonds in the environment of the first named atom. Some
            users may wish to give only the symmetry-independent
            distances and supply a multiplicity to indicate how many
            such bonds are found in the atomic environment.
  </td></tr>
  <tr><td>
<pre><code>
loop_
_geom_bond_atom_site_label_1
_geom_bond_atom_site_label_2
_geom_bond_site_symmetry_2
_geom_bond_distance
_geom_bond_multiplicity
Ca1   F1   1_555  2.495(9)    1
Ca1   F2   1_555  2.291(10)   2
Ca1   F2   2_555  2.291(10)   0
Ca1   F2   3_565  2.391(11)   2
Ca1   F2   4_555  2.391(11)   0
Ca1   F3   2_545  2.214(11)   2
Ca1   F3   5_555  2.214(11)   0
Cr1   F1   1_555  1.940(11)   2
Cr1   F1   2_555  1.940(11)   0
Cr1   F2   1_555  1.918(9)    2
Cr1   F2   2_555  1.918(9)    0
Cr1   F3   1_555  1.848(10)   2
Cr1   F3   2_555  1.848(10)   0
</code></pre>
  </td><td>Example 3 - The same structure as in Example 2, but where the
            multiplicity is given with a full bond list. Note the
            use of a value of 0 for _geom_bond_multiplicity in
            such a case.
  </td></tr>
</table>
### <a name="_geom_bond_atom_site_label_1"></a>\_geom\_bond\_atom\_site\_label\_1

The labels of two atom sites that form a bond. These must match
 labels specified as [\_atom\_site\_label](#_atom_site_label) in the atom list.

### <a name="_geom_bond_atom_site_label_2"></a>\_geom\_bond\_atom\_site\_label\_2

The labels of two atom sites that form a bond. These must match
 labels specified as [\_atom\_site\_label](#_atom_site_label) in the atom list.

### <a name="_geom_bond_distance"></a>\_geom\_bond\_distance

The intramolecular bond distance in angstroms.

Units: angstroms

### <a name="_geom_bond_multiplicity"></a>\_geom\_bond\_multiplicity

The number of times the given bond appears in the environment
 of the atoms labelled \_geom\_bond\_atom\_site\_label\_1. In cases
 where the full list of bonds is given, one of the series of
 equivalent bonds may be assigned the appropriate multiplicity
 while the others are assigned a value of 0.

Default value: '1'

### <a name="_geom_bond_publ_flag"></a>\_geom\_bond\_publ\_flag

This code signals whether the bond distance is referred to in a
 publication or should be placed in a list of significant bond
 distances.

Values:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>no</td><td>do not include bond in special list</td></tr>
  <tr><td>n</td><td>abbreviation for &quot;no&quot;</td></tr>
  <tr><td>yes</td><td>do include bond in special list</td></tr>
  <tr><td>y</td><td>abbreviation for &quot;yes&quot;</td></tr>
</table>
Default value: 'no'

### <a name="_geom_bond_site_symmetry_1"></a>\_geom\_bond\_site\_symmetry\_1

The symmetry code of each atom site as the symmetry-equivalent
 position number &#39;n&#39; and the cell translation number &#39;klm&#39;.
 These numbers are combined to form the code &#39;n klm&#39; or n\_klm.
 The character string n\_klm is composed as follows:

 n refers to the symmetry operation that is applied to the
 coordinates stored in [\_atom\_site\_fract\_x](#_atom_site_fract_x), [\_atom\_site\_fract\_y](#_atom_site_fract_y)
 and [\_atom\_site\_fract\_z](#_atom_site_fract_z). It must match a number given in
 [\_space\_group\_symop\_id](#_space_group_symop_id).

 k, l and m refer to the translations that are subsequently
 applied to the symmetry-transformed coordinates to generate
 the atom used in calculating the bond. These translations
 (x,y,z) are related to (k,l,m) by the relations
      k = 5 + x
      l = 5 + y
      m = 5 + z
 By adding 5 to the translations, the use of negative numbers
 is avoided.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
.
  </td><td>no symmetry or translation to site
  </td></tr>
  <tr><td>
4
  </td><td>4th symmetry operation applied
  </td></tr>
  <tr><td>
7_645
  </td><td>7th symm. posn.; +a on x; -b on y
  </td></tr>
</table>
### <a name="_geom_bond_site_symmetry_2"></a>\_geom\_bond\_site\_symmetry\_2

The symmetry code of each atom site as the symmetry-equivalent
 position number &#39;n&#39; and the cell translation number &#39;klm&#39;.
 These numbers are combined to form the code &#39;n klm&#39; or n\_klm.
 The character string n\_klm is composed as follows:

 n refers to the symmetry operation that is applied to the
 coordinates stored in [\_atom\_site\_fract\_x](#_atom_site_fract_x), [\_atom\_site\_fract\_y](#_atom_site_fract_y)
 and [\_atom\_site\_fract\_z](#_atom_site_fract_z). It must match a number given in
 [\_space\_group\_symop\_id](#_space_group_symop_id).

 k, l and m refer to the translations that are subsequently
 applied to the symmetry-transformed coordinates to generate
 the atom used in calculating the bond. These translations
 (x,y,z) are related to (k,l,m) by the relations
      k = 5 + x
      l = 5 + y
      m = 5 + z
 By adding 5 to the translations, the use of negative numbers
 is avoided.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
.
  </td><td>no symmetry or translation to site
  </td></tr>
  <tr><td>
4
  </td><td>4th symmetry operation applied
  </td></tr>
  <tr><td>
7_645
  </td><td>7th symm. posn.; +a on x; -b on y
  </td></tr>
</table>
### <a name="_geom_bond_valence"></a>\_geom\_bond\_valence

The bond valence calculated from [\_geom\_bond\_distance](#_geom_bond_distance).

## <a name="GEOM_CONTACT"></a>GEOM\_CONTACT

Data items in the GEOM\_CONTACT category record details about
 interatomic contacts as calculated from the
 ATOM, CELL and SYMMETRY data.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
 _geom_contact_atom_site_label_1
 _geom_contact_atom_site_label_2
 _geom_contact_distance
 _geom_contact_site_symmetry_1
 _geom_contact_site_symmetry_2
 _geom_contact_publ_flag
 O(1)  O(2)     2.735(3)  .  .  yes
 H(O1) O(2)     1.82      .  .  no
</code></pre>
  </td><td>Example 1 - based on data set CLPHO6 of Ferguson, Ruhl, McKervey &amp; Browne
            [Acta Cryst. (1992), C48, 2262-2264].
  </td></tr>
</table>
### <a name="_geom_contact_atom_site_label_1"></a>\_geom\_contact\_atom\_site\_label\_1

The labels of two atom sites that are within contact distance.
 The labels must match [\_atom\_site\_label](#_atom_site_label) codes in the atom list.

### <a name="_geom_contact_atom_site_label_2"></a>\_geom\_contact\_atom\_site\_label\_2

The labels of two atom sites that are within contact distance.
 The labels must match [\_atom\_site\_label](#_atom_site_label) codes in the atom list.

### <a name="_geom_contact_distance"></a>\_geom\_contact\_distance

The interatomic contact distance in angstroms.

Units: angstroms

### <a name="_geom_contact_publ_flag"></a>\_geom\_contact\_publ\_flag

This code signals whether the contact distance is referred to
 in a publication or should be placed in a list of significant
 contact distances.

Values:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>no</td><td>do not include distance in special list</td></tr>
  <tr><td>n</td><td>abbreviation for &quot;no&quot;</td></tr>
  <tr><td>yes</td><td>do include distance in special list</td></tr>
  <tr><td>y</td><td>abbreviation for &quot;yes&quot;</td></tr>
</table>
Default value: 'no'

### <a name="_geom_contact_site_symmetry_1"></a>\_geom\_contact\_site\_symmetry\_1

The symmetry code of each atom site as the symmetry-equivalent
 position number &#39;n&#39; and the cell translation number &#39;klm&#39;.
 These numbers are combined to form the code &#39;n klm&#39; or n\_klm.
 The character string n\_klm is composed as follows:

 n refers to the symmetry operation that is applied to the
 coordinates stored in [\_atom\_site\_fract\_x](#_atom_site_fract_x), [\_atom\_site\_fract\_y](#_atom_site_fract_y)
 and [\_atom\_site\_fract\_z](#_atom_site_fract_z). It must match a number given in
 [\_space\_group\_symop\_id](#_space_group_symop_id).

 k, l and m refer to the translations that are subsequently
 applied to the symmetry-transformed coordinates to generate
 the atom used in calculating the contact. These translations
 (x,y,z) are related to (k,l,m) by the relations
      k = 5 + x
      l = 5 + y
      m = 5 + z
 By adding 5 to the translations, the use of negative numbers
 is avoided.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
.
  </td><td>no symmetry or translation to site
  </td></tr>
  <tr><td>
4
  </td><td>4th symmetry operation applied
  </td></tr>
  <tr><td>
7_645
  </td><td>7th symm. posn.; +a on x; -b on y
  </td></tr>
</table>
### <a name="_geom_contact_site_symmetry_2"></a>\_geom\_contact\_site\_symmetry\_2

The symmetry code of each atom site as the symmetry-equivalent
 position number &#39;n&#39; and the cell translation number &#39;klm&#39;.
 These numbers are combined to form the code &#39;n klm&#39; or n\_klm.
 The character string n\_klm is composed as follows:

 n refers to the symmetry operation that is applied to the
 coordinates stored in [\_atom\_site\_fract\_x](#_atom_site_fract_x), [\_atom\_site\_fract\_y](#_atom_site_fract_y)
 and [\_atom\_site\_fract\_z](#_atom_site_fract_z). It must match a number given in
 [\_space\_group\_symop\_id](#_space_group_symop_id).

 k, l and m refer to the translations that are subsequently
 applied to the symmetry-transformed coordinates to generate
 the atom used in calculating the contact. These translations
 (x,y,z) are related to (k,l,m) by the relations
      k = 5 + x
      l = 5 + y
      m = 5 + z
 By adding 5 to the translations, the use of negative numbers
 is avoided.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
.
  </td><td>no symmetry or translation to site
  </td></tr>
  <tr><td>
4
  </td><td>4th symmetry operation applied
  </td></tr>
  <tr><td>
7_645
  </td><td>7th symm. posn.; +a on x; -b on y
  </td></tr>
</table>
## <a name="GEOM_HBOND"></a>GEOM\_HBOND

Data items in the GEOM\_HBOND category record details about
 hydrogen bonds as calculated from the ATOM,
 CELL and SYMMETRY data.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
_geom_hbond_atom_site_label_D
_geom_hbond_atom_site_label_H
_geom_hbond_atom_site_label_A
_geom_hbond_distance_DH
_geom_hbond_distance_HA
_geom_hbond_distance_DA
_geom_hbond_angle_DHA
_geom_hbond_publ_flag

N6   HN6  OW   0.888(8)  1.921(12)  2.801(8)  169.6(8)  yes
OW   HO2  O7   0.917(6)  1.923(12)  2.793(8)  153.5(8)  yes
OW   HO1  N10  0.894(8)  1.886(11)  2.842(8)  179.7(9)  yes
</code></pre>
  </td><td>Example 1 - based on C~14~H~13~ClN~2~O.H~2~O, reported by Palmer,
            Puddle &amp; Lisgarten [Acta Cryst. (1993), C49, 1777-1779].
  </td></tr>
</table>
### <a name="_geom_hbond_angle_DHA"></a>\_geom\_hbond\_angle\_DHA

Angle in degrees defined by the three sites
 [\_geom\_hbond\_atom\_site\_label\_D](#_geom_hbond_atom_site_label_D), \*\_H and \*\_A. The site at \*\_H
 (the hydrogen atom participating in the interaction) is at
 the apex of the angle.

Units: degrees

### <a name="_geom_hbond_atom_site_label_D"></a>\_geom\_hbond\_atom\_site\_label\_D

The labels of three atom sites (respectively, the donor atom,
 hydrogen atom and acceptor atom) participating in a hydrogen
 bond. These must match labels specified as [\_atom\_site\_label](#_atom_site_label)
 in the atom list.

### <a name="_geom_hbond_atom_site_label_H"></a>\_geom\_hbond\_atom\_site\_label\_H

The labels of three atom sites (respectively, the donor atom,
 hydrogen atom and acceptor atom) participating in a hydrogen
 bond. These must match labels specified as [\_atom\_site\_label](#_atom_site_label)
 in the atom list.

### <a name="_geom_hbond_atom_site_label_A"></a>\_geom\_hbond\_atom\_site\_label\_A

The labels of three atom sites (respectively, the donor atom,
 hydrogen atom and acceptor atom) participating in a hydrogen
 bond. These must match labels specified as [\_atom\_site\_label](#_atom_site_label)
 in the atom list.

### <a name="_geom_hbond_distance_DH"></a>\_geom\_hbond\_distance\_DH

Distances in angstroms between the donor and hydrogen (\*\_DH),
 hydrogen and acceptor (\*\_HA) and donor and acceptor (\*\_DA)
 sites in a hydrogen bond.

Units: angstroms

### <a name="_geom_hbond_distance_HA"></a>\_geom\_hbond\_distance\_HA

Distances in angstroms between the donor and hydrogen (\*\_DH),
 hydrogen and acceptor (\*\_HA) and donor and acceptor (\*\_DA)
 sites in a hydrogen bond.

Units: angstroms

### <a name="_geom_hbond_distance_DA"></a>\_geom\_hbond\_distance\_DA

Distances in angstroms between the donor and hydrogen (\*\_DH),
 hydrogen and acceptor (\*\_HA) and donor and acceptor (\*\_DA)
 sites in a hydrogen bond.

Units: angstroms

### <a name="_geom_hbond_publ_flag"></a>\_geom\_hbond\_publ\_flag

This code signals whether the hydrogen-bond information
 is referred to in a publication or should be placed in a
 table of significant hydrogen-bond geometry.

Values:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>no</td><td>do not include bond in special list</td></tr>
  <tr><td>n</td><td>abbreviation for &quot;no&quot;</td></tr>
  <tr><td>yes</td><td>do include bond in special list</td></tr>
  <tr><td>y</td><td>abbreviation for &quot;yes&quot;</td></tr>
</table>
Default value: 'no'

### <a name="_geom_hbond_site_symmetry_D"></a>\_geom\_hbond\_site\_symmetry\_D

The symmetry code of each atom site as the symmetry-equivalent
 position number &#39;n&#39; and the cell translation number &#39;klm&#39;.
 These numbers are combined to form the code &#39;n klm&#39; or n\_klm.
 The character string n\_klm is composed as follows:

 n refers to the symmetry operation that is applied to the
 coordinates stored in [\_atom\_site\_fract\_x](#_atom_site_fract_x), [\_atom\_site\_fract\_y](#_atom_site_fract_y)
 and [\_atom\_site\_fract\_z](#_atom_site_fract_z). It must match a number given in
 [\_space\_group\_symop\_id](#_space_group_symop_id).

 k, l and m refer to the translations that are subsequently
 applied to the symmetry-transformed coordinates to generate
 the atom used in calculating the hydrogen bond. These
 translations (x,y,z) are related to (k,l,m) by the relations
      k = 5 + x
      l = 5 + y
      m = 5 + z
 By adding 5 to the translations, the use of negative numbers
 is avoided.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
.
  </td><td>no symmetry or translation to site
  </td></tr>
  <tr><td>
4
  </td><td>4th symmetry operation applied
  </td></tr>
  <tr><td>
7_645
  </td><td>7th symm. posn.; +a on x; -b on y
  </td></tr>
</table>
### <a name="_geom_hbond_site_symmetry_H"></a>\_geom\_hbond\_site\_symmetry\_H

The symmetry code of each atom site as the symmetry-equivalent
 position number &#39;n&#39; and the cell translation number &#39;klm&#39;.
 These numbers are combined to form the code &#39;n klm&#39; or n\_klm.
 The character string n\_klm is composed as follows:

 n refers to the symmetry operation that is applied to the
 coordinates stored in [\_atom\_site\_fract\_x](#_atom_site_fract_x), [\_atom\_site\_fract\_y](#_atom_site_fract_y)
 and [\_atom\_site\_fract\_z](#_atom_site_fract_z). It must match a number given in
 [\_space\_group\_symop\_id](#_space_group_symop_id).

 k, l and m refer to the translations that are subsequently
 applied to the symmetry-transformed coordinates to generate
 the atom used in calculating the hydrogen bond. These
 translations (x,y,z) are related to (k,l,m) by the relations
      k = 5 + x
      l = 5 + y
      m = 5 + z
 By adding 5 to the translations, the use of negative numbers
 is avoided.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
.
  </td><td>no symmetry or translation to site
  </td></tr>
  <tr><td>
4
  </td><td>4th symmetry operation applied
  </td></tr>
  <tr><td>
7_645
  </td><td>7th symm. posn.; +a on x; -b on y
  </td></tr>
</table>
### <a name="_geom_hbond_site_symmetry_A"></a>\_geom\_hbond\_site\_symmetry\_A

The symmetry code of each atom site as the symmetry-equivalent
 position number &#39;n&#39; and the cell translation number &#39;klm&#39;.
 These numbers are combined to form the code &#39;n klm&#39; or n\_klm.
 The character string n\_klm is composed as follows:

 n refers to the symmetry operation that is applied to the
 coordinates stored in [\_atom\_site\_fract\_x](#_atom_site_fract_x), [\_atom\_site\_fract\_y](#_atom_site_fract_y)
 and [\_atom\_site\_fract\_z](#_atom_site_fract_z). It must match a number given in
 [\_space\_group\_symop\_id](#_space_group_symop_id).

 k, l and m refer to the translations that are subsequently
 applied to the symmetry-transformed coordinates to generate
 the atom used in calculating the hydrogen bond. These
 translations (x,y,z) are related to (k,l,m) by the relations
      k = 5 + x
      l = 5 + y
      m = 5 + z
 By adding 5 to the translations, the use of negative numbers
 is avoided.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
.
  </td><td>no symmetry or translation to site
  </td></tr>
  <tr><td>
4
  </td><td>4th symmetry operation applied
  </td></tr>
  <tr><td>
7_645
  </td><td>7th symm. posn.; +a on x; -b on y
  </td></tr>
</table>
## <a name="GEOM_TORSION"></a>GEOM\_TORSION

Data items in the GEOM\_TORSION category record details about
 interatomic torsion angles as calculated from
 the ATOM, CELL and SYMMETRY data.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
 _geom_torsion_atom_site_label_1
 _geom_torsion_atom_site_label_2
 _geom_torsion_atom_site_label_3
 _geom_torsion_atom_site_label_4
 _geom_torsion
 _geom_torsion_site_symmetry_1
 _geom_torsion_site_symmetry_2
 _geom_torsion_site_symmetry_3
 _geom_torsion_site_symmetry_4
 _geom_torsion_publ_flag
 C(9)  O(2)  C(7)   C(2)    71.8(2)  .  .  .  .      yes
 C(7)  O(2)  C(9)   C(10) -168.0(3)  .  .  .  2_666  yes
 C(10) O(3)  C(8)   C(6)  -167.7(3)  .  .  .  .      yes
 C(8)  O(3)  C(10)  C(9)   -69.7(2)  .  .  .  2_666  yes
 O(1)  C(1)  C(2)   C(3)  -179.5(4)  .  .  .  .      no
 O(1)  C(1)  C(2)   C(7)    -0.6(1)  .  .  .  .      no
</code></pre>
  </td><td>Example 1 - based on data set CLPHO6 of Ferguson, Ruhl, McKervey &amp; Browne
           [Acta Cryst. (1992), C48, 2262-2264].
  </td></tr>
</table>
### <a name="_geom_torsion"></a>\_geom\_torsion

The torsion angle in degrees bounded by the four atom sites
 identified by the \_geom\_torsion\_atom\_site\_label\_ codes. These
 must match labels specified as [\_atom\_site\_label](#_atom_site_label) in the atom list.
 The torsion-angle definition should be that of Klyne and Prelog.

 Ref: Klyne, W. &amp; Prelog, V. (1960). Experientia, 16, 521-523.

Units: degrees

### <a name="_geom_torsion_atom_site_label_1"></a>\_geom\_torsion\_atom\_site\_label\_1

The labels of the four atom sites which define the torsion angle
 specified by [\_geom\_torsion](#_geom_torsion). These must match codes specified as
 [\_atom\_site\_label](#_atom_site_label) in the atom list. The torsion-angle definition
 should be that of Klyne and Prelog. The vector direction
 \*\_label\_2 to \*\_label\_3 is the viewing direction, and the torsion
 angle is the angle of twist required to superimpose the
 projection of the vector between site 2 and site 1 onto the
 projection of the vector between site 3 and site 4. Clockwise
 torsions are positive, anticlockwise torsions are negative.

 Ref: Klyne, W. &amp; Prelog, V. (1960). Experientia, 16, 521-523.

### <a name="_geom_torsion_atom_site_label_2"></a>\_geom\_torsion\_atom\_site\_label\_2

The labels of the four atom sites which define the torsion angle
 specified by [\_geom\_torsion](#_geom_torsion). These must match codes specified as
 [\_atom\_site\_label](#_atom_site_label) in the atom list. The torsion-angle definition
 should be that of Klyne and Prelog. The vector direction
 \*\_label\_2 to \*\_label\_3 is the viewing direction, and the torsion
 angle is the angle of twist required to superimpose the
 projection of the vector between site 2 and site 1 onto the
 projection of the vector between site 3 and site 4. Clockwise
 torsions are positive, anticlockwise torsions are negative.

 Ref: Klyne, W. &amp; Prelog, V. (1960). Experientia, 16, 521-523.

### <a name="_geom_torsion_atom_site_label_3"></a>\_geom\_torsion\_atom\_site\_label\_3

The labels of the four atom sites which define the torsion angle
 specified by [\_geom\_torsion](#_geom_torsion). These must match codes specified as
 [\_atom\_site\_label](#_atom_site_label) in the atom list. The torsion-angle definition
 should be that of Klyne and Prelog. The vector direction
 \*\_label\_2 to \*\_label\_3 is the viewing direction, and the torsion
 angle is the angle of twist required to superimpose the
 projection of the vector between site 2 and site 1 onto the
 projection of the vector between site 3 and site 4. Clockwise
 torsions are positive, anticlockwise torsions are negative.

 Ref: Klyne, W. &amp; Prelog, V. (1960). Experientia, 16, 521-523.

### <a name="_geom_torsion_atom_site_label_4"></a>\_geom\_torsion\_atom\_site\_label\_4

The labels of the four atom sites which define the torsion angle
 specified by [\_geom\_torsion](#_geom_torsion). These must match codes specified as
 [\_atom\_site\_label](#_atom_site_label) in the atom list. The torsion-angle definition
 should be that of Klyne and Prelog. The vector direction
 \*\_label\_2 to \*\_label\_3 is the viewing direction, and the torsion
 angle is the angle of twist required to superimpose the
 projection of the vector between site 2 and site 1 onto the
 projection of the vector between site 3 and site 4. Clockwise
 torsions are positive, anticlockwise torsions are negative.

 Ref: Klyne, W. &amp; Prelog, V. (1960). Experientia, 16, 521-523.

### <a name="_geom_torsion_publ_flag"></a>\_geom\_torsion\_publ\_flag

This code signals whether the torsion angle is referred to in a
 publication or should be placed in a table of significant
 torsion angles.

Values:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>no</td><td>do not include angle in special list</td></tr>
  <tr><td>n</td><td>abbreviation for &quot;no&quot;</td></tr>
  <tr><td>yes</td><td>do include angle in special list</td></tr>
  <tr><td>y</td><td>abbreviation for &quot;yes&quot;</td></tr>
</table>
Default value: 'no'

### <a name="_geom_torsion_site_symmetry_1"></a>\_geom\_torsion\_site\_symmetry\_1

The symmetry code of each atom site as the symmetry-equivalent
 position number &#39;n&#39; and the cell translation number &#39;klm&#39;.
 These numbers are combined to form the code &#39;n klm&#39; or n\_klm.
 The character string n\_klm is composed as follows:

 n refers to the symmetry operation that is applied to the
 coordinates stored in [\_atom\_site\_fract\_x](#_atom_site_fract_x), [\_atom\_site\_fract\_y](#_atom_site_fract_y)
 and [\_atom\_site\_fract\_z](#_atom_site_fract_z). It must match a number given in
 [\_space\_group\_symop\_id](#_space_group_symop_id).

 k, l and m refer to the translations that are subsequently
 applied to the symmetry-transformed coordinates to generate
 the atom used in calculating the angle. These translations
 (x,y,z) are related to (k,l,m) by the relations
      k = 5 + x
      l = 5 + y
      m = 5 + z
 By adding 5 to the translations, the use of negative numbers
 is avoided.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
.
  </td><td>no symmetry or translation to site
  </td></tr>
  <tr><td>
4
  </td><td>4th symmetry operation applied
  </td></tr>
  <tr><td>
7_645
  </td><td>7th symm. posn.; +a on x; -b on y
  </td></tr>
</table>
### <a name="_geom_torsion_site_symmetry_2"></a>\_geom\_torsion\_site\_symmetry\_2

The symmetry code of each atom site as the symmetry-equivalent
 position number &#39;n&#39; and the cell translation number &#39;klm&#39;.
 These numbers are combined to form the code &#39;n klm&#39; or n\_klm.
 The character string n\_klm is composed as follows:

 n refers to the symmetry operation that is applied to the
 coordinates stored in [\_atom\_site\_fract\_x](#_atom_site_fract_x), [\_atom\_site\_fract\_y](#_atom_site_fract_y)
 and [\_atom\_site\_fract\_z](#_atom_site_fract_z). It must match a number given in
 [\_space\_group\_symop\_id](#_space_group_symop_id).

 k, l and m refer to the translations that are subsequently
 applied to the symmetry-transformed coordinates to generate
 the atom used in calculating the angle. These translations
 (x,y,z) are related to (k,l,m) by the relations
      k = 5 + x
      l = 5 + y
      m = 5 + z
 By adding 5 to the translations, the use of negative numbers
 is avoided.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
.
  </td><td>no symmetry or translation to site
  </td></tr>
  <tr><td>
4
  </td><td>4th symmetry operation applied
  </td></tr>
  <tr><td>
7_645
  </td><td>7th symm. posn.; +a on x; -b on y
  </td></tr>
</table>
### <a name="_geom_torsion_site_symmetry_3"></a>\_geom\_torsion\_site\_symmetry\_3

The symmetry code of each atom site as the symmetry-equivalent
 position number &#39;n&#39; and the cell translation number &#39;klm&#39;.
 These numbers are combined to form the code &#39;n klm&#39; or n\_klm.
 The character string n\_klm is composed as follows:

 n refers to the symmetry operation that is applied to the
 coordinates stored in [\_atom\_site\_fract\_x](#_atom_site_fract_x), [\_atom\_site\_fract\_y](#_atom_site_fract_y)
 and [\_atom\_site\_fract\_z](#_atom_site_fract_z). It must match a number given in
 [\_space\_group\_symop\_id](#_space_group_symop_id).

 k, l and m refer to the translations that are subsequently
 applied to the symmetry-transformed coordinates to generate
 the atom used in calculating the angle. These translations
 (x,y,z) are related to (k,l,m) by the relations
      k = 5 + x
      l = 5 + y
      m = 5 + z
 By adding 5 to the translations, the use of negative numbers
 is avoided.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
.
  </td><td>no symmetry or translation to site
  </td></tr>
  <tr><td>
4
  </td><td>4th symmetry operation applied
  </td></tr>
  <tr><td>
7_645
  </td><td>7th symm. posn.; +a on x; -b on y
  </td></tr>
</table>
### <a name="_geom_torsion_site_symmetry_4"></a>\_geom\_torsion\_site\_symmetry\_4

The symmetry code of each atom site as the symmetry-equivalent
 position number &#39;n&#39; and the cell translation number &#39;klm&#39;.
 These numbers are combined to form the code &#39;n klm&#39; or n\_klm.
 The character string n\_klm is composed as follows:

 n refers to the symmetry operation that is applied to the
 coordinates stored in [\_atom\_site\_fract\_x](#_atom_site_fract_x), [\_atom\_site\_fract\_y](#_atom_site_fract_y)
 and [\_atom\_site\_fract\_z](#_atom_site_fract_z). It must match a number given in
 [\_space\_group\_symop\_id](#_space_group_symop_id).

 k, l and m refer to the translations that are subsequently
 applied to the symmetry-transformed coordinates to generate
 the atom used in calculating the angle. These translations
 (x,y,z) are related to (k,l,m) by the relations
      k = 5 + x
      l = 5 + y
      m = 5 + z
 By adding 5 to the translations, the use of negative numbers
 is avoided.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
.
  </td><td>no symmetry or translation to site
  </td></tr>
  <tr><td>
4
  </td><td>4th symmetry operation applied
  </td></tr>
  <tr><td>
7_645
  </td><td>7th symm. posn.; +a on x; -b on y
  </td></tr>
</table>
## <a name="JOURNAL"></a>JOURNAL

Data items in the JOURNAL category record details about the
 book-keeping by the journal staff when processing
 a CIF submitted for publication.

 The creator of a CIF will not normally specify these data items.
 The data names are not defined in the dictionary because they are
 for journal use only.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
_journal_date_recd_electronic     91-04-15
_journal_date_from_coeditor       91-04-18
_journal_date_accepted            91-04-18
_journal_date_printers_first      91-08-07
_journal_date_proofs_out          91-08-07
_journal_coeditor_code            HL0007
_journal_techeditor_code          C910963
_journal_coden_ASTM               ACSCEE
_journal_name_full        &#39;Acta Crystallographica Section C&#39;
_journal_year                     1991
_journal_volume                   47
_journal_issue                    NOV91
_journal_page_first               2276
_journal_page_last                2277
</code></pre>
  </td><td>Example 1 - based on Acta Cryst. file for entry HL0007 [Willis, Beckwith
            &amp; Tozer (1991). Acta Cryst. C47, 2276-2277].
  </td></tr>
</table>
### <a name="_journal_coden_ASTM"></a>\_journal\_coden\_ASTM

Data items specified by the journal staff.

### <a name="_journal_coden_Cambridge"></a>\_journal\_coden\_Cambridge

Data items specified by the journal staff.

### <a name="_journal_coeditor_address"></a>\_journal\_coeditor\_address

Data items specified by the journal staff.

### <a name="_journal_coeditor_code"></a>\_journal\_coeditor\_code

Data items specified by the journal staff.

### <a name="_journal_coeditor_email"></a>\_journal\_coeditor\_email

Data items specified by the journal staff.

### <a name="_journal_coeditor_fax"></a>\_journal\_coeditor\_fax

Data items specified by the journal staff.

### <a name="_journal_coeditor_name"></a>\_journal\_coeditor\_name

Data items specified by the journal staff.

### <a name="_journal_coeditor_notes"></a>\_journal\_coeditor\_notes

Data items specified by the journal staff.

### <a name="_journal_coeditor_phone"></a>\_journal\_coeditor\_phone

Data items specified by the journal staff.

### <a name="_journal_data_validation_number"></a>\_journal\_data\_validation\_number

Data items specified by the journal staff.

### <a name="_journal_date_accepted"></a>\_journal\_date\_accepted

Data items specified by the journal staff.

### <a name="_journal_date_from_coeditor"></a>\_journal\_date\_from\_coeditor

Data items specified by the journal staff.

### <a name="_journal_date_to_coeditor"></a>\_journal\_date\_to\_coeditor

Data items specified by the journal staff.

### <a name="_journal_date_printers_final"></a>\_journal\_date\_printers\_final

Data items specified by the journal staff.

### <a name="_journal_date_printers_first"></a>\_journal\_date\_printers\_first

Data items specified by the journal staff.

### <a name="_journal_date_proofs_in"></a>\_journal\_date\_proofs\_in

Data items specified by the journal staff.

### <a name="_journal_date_proofs_out"></a>\_journal\_date\_proofs\_out

Data items specified by the journal staff.

### <a name="_journal_date_recd_copyright"></a>\_journal\_date\_recd\_copyright

Data items specified by the journal staff.

### <a name="_journal_date_recd_electronic"></a>\_journal\_date\_recd\_electronic

Data items specified by the journal staff.

### <a name="_journal_date_recd_hard_copy"></a>\_journal\_date\_recd\_hard\_copy

Data items specified by the journal staff.

### <a name="_journal_issue"></a>\_journal\_issue

Data items specified by the journal staff.

### <a name="_journal_language"></a>\_journal\_language

Data items specified by the journal staff.

### <a name="_journal_name_full"></a>\_journal\_name\_full

Data items specified by the journal staff.

### <a name="_journal_page_first"></a>\_journal\_page\_first

Data items specified by the journal staff.

### <a name="_journal_page_last"></a>\_journal\_page\_last

Data items specified by the journal staff.

### <a name="_journal_paper_category"></a>\_journal\_paper\_category

Data items specified by the journal staff.

### <a name="_journal_suppl_publ_number"></a>\_journal\_suppl\_publ\_number

Data items specified by the journal staff.

### <a name="_journal_suppl_publ_pages"></a>\_journal\_suppl\_publ\_pages

Data items specified by the journal staff.

### <a name="_journal_techeditor_address"></a>\_journal\_techeditor\_address

Data items specified by the journal staff.

### <a name="_journal_techeditor_code"></a>\_journal\_techeditor\_code

Data items specified by the journal staff.

### <a name="_journal_techeditor_email"></a>\_journal\_techeditor\_email

Data items specified by the journal staff.

### <a name="_journal_techeditor_fax"></a>\_journal\_techeditor\_fax

Data items specified by the journal staff.

### <a name="_journal_techeditor_name"></a>\_journal\_techeditor\_name

Data items specified by the journal staff.

### <a name="_journal_techeditor_notes"></a>\_journal\_techeditor\_notes

Data items specified by the journal staff.

### <a name="_journal_techeditor_phone"></a>\_journal\_techeditor\_phone

Data items specified by the journal staff.

### <a name="_journal_volume"></a>\_journal\_volume

Data items specified by the journal staff.

### <a name="_journal_year"></a>\_journal\_year

Data items specified by the journal staff.

## <a name="JOURNAL_INDEX"></a>JOURNAL\_INDEX

Data items in the JOURNAL\_INDEX category are used to list
 terms used to generate the journal indexes.

 The creator of a CIF will not normally specify these data items.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
_journal_index_type
_journal_index_term
_journal_index_subterm
  O   C16H19NO4            .
  S   alkaloids           (-)-norcocaine
  S   (-)-norcocaine       .
  S
;  [2R,3S-(2&beta;,3&beta;)]-methyl
   3-(benzoyloxy)-8-azabicyclo[3.2.1]octane-2-carboxylate
;                          .
</code></pre>
  </td><td>Example 1 - based on a paper by Zhu, Reynolds, Klein &amp; Trudell
            [Acta Cryst. (1994), C50, 2067-2069].
  </td></tr>
</table>
### <a name="_journal_index_subterm"></a>\_journal\_index\_subterm

Indexing terms supplied by the journal staff.

### <a name="_journal_index_term"></a>\_journal\_index\_term

Indexing terms supplied by the journal staff.

### <a name="_journal_index_type"></a>\_journal\_index\_type

Indexing terms supplied by the journal staff.

## <a name="PUBL"></a>PUBL

Data items in the PUBL category are used when submitting a
 manuscript for publication. They refer either to the paper as
 a whole, or to specific named elements within a paper (such as
 the title and abstract, or the Comment and Experimental
 sections of Acta Crystallographica Section C). The data items
 in the PUBL\_BODY category should be used for the text
 of other submissions. Typically, each journal will
 supply a list of the specific items it requires in its Notes
 for Authors.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
_publ_section_title
;  trans-3-Benzoyl-2-(tert-butyl)-4-(iso-butyl)-
   1,3-oxazolidin-5-one
;

_publ_section_abstract
;  The oxazolidinone ring is a shallow envelope
   conformation with the tert-butyl and iso-butyl groups
   occupying trans-positions with respect to the ring. The
   angles at the N atom sum to 356.2&deg;, indicating a very
   small degree of pyramidalization at this atom. This is
   consistent with electron delocalization between the N
   atom and the carbonyl centre [N-C=O = 1.374(3)&Aring;].
;
</code></pre>
  </td><td>Example 1 - based on Willis, Beckwith &amp; Tozer
            [Acta Cryst. (1991), C47, 2276-2277].
  </td></tr>
  <tr><td>
<pre><code>
_publ_section_title
;  Hemiasterlin methyl ester
;

_publ_section_title_footnote
;  IUPAC name: methyl 2,5-dimethyl-4-{2-[3-methyl-
   2-methylamino-3-(N-methylbenzo[b]pyrrol-
   3-yl)butanamido]-3,3-dimethyl-N-methyl-
   butanamido}-2-hexenoate.
;
</code></pre>
  </td><td>Example 2 - based on C~31~H~48~N~4~O~4~, reported by Coleman, Patrick,
            Andersen &amp; Rettig [Acta Cryst. (1996), C52, 1525-1527].
  </td></tr>
</table>
### <a name="_publ_contact_author"></a>\_publ\_contact\_author

The name and address of the author submitting the manuscript and
 data block. This is the person contacted by the journal
 editorial staff. It is preferable to use the separate data items
 [\_publ\_contact\_author\_name](#_publ_contact_author_name) and [\_publ\_contact\_author\_address](#_publ_contact_author_address).

### <a name="_publ_contact_author_address"></a>\_publ\_contact\_author\_address

The address of the author submitting the manuscript and
 data block. This is the person contacted by the journal
 editorial staff.

### <a name="_publ_contact_author_email"></a>\_publ\_contact\_author\_email

E-mail address in a form recognizable to international networks.
 The format of e-mail addresses is given in Section 3.4, Address 
 Specification, of  Internet Message Format, RFC 2822, P. Resnick 
 (Editor), Network Standards Group, April 2001.

### <a name="_publ_contact_author_fax"></a>\_publ\_contact\_author\_fax

Facsimile telephone number of the author submitting the
 manuscript and data block.

 The recommended style is the international dialing
 prefix, followed  by the area code in parentheses, followed by
 the local number with no spaces. The earlier convention of
 including the international dialing prefix in parentheses is
 no longer recommended.

### <a name="_publ_contact_author_id_iucr"></a>\_publ\_contact\_author\_id\_iucr

Identifier in the IUCr contact database of the author
 submitting the manuscript and data block. This identifier may
 be available from the World Directory of Crystallographers
 ([http://wdc.iucr.org](http://wdc.iucr.org)).

### <a name="_publ_contact_author_name"></a>\_publ\_contact\_author\_name

The name of the author submitting the manuscript and
 data block. This is the person contacted by the journal
 editorial staff.

### <a name="_publ_contact_author_phone"></a>\_publ\_contact\_author\_phone

Telephone number of the author submitting the manuscript and
 data block.

 The recommended style is the international dialing
 prefix, followed by the area code in parentheses, followed by the
 local number and any extension number prefixed by &#39;x&#39;,
 with no spaces. The earlier convention of including
 the international dialing prefix in parentheses is no longer
 recommended.

### <a name="_publ_contact_letter"></a>\_publ\_contact\_letter

A letter submitted to the journal editor by the contact author.

### <a name="_publ_manuscript_creation"></a>\_publ\_manuscript\_creation

A description of the word-processor package and computer used to
 create the word-processed manuscript stored as
 [\_publ\_manuscript\_processed](#_publ_manuscript_processed).

### <a name="_publ_manuscript_processed"></a>\_publ\_manuscript\_processed

The full manuscript of a paper (excluding possibly the figures
 and the tables) output in ASCII characters from a word processor.
 Information about the generation of this data item must be
 specified in the data item [\_publ\_manuscript\_creation](#_publ_manuscript_creation).

### <a name="_publ_manuscript_text"></a>\_publ\_manuscript\_text

The full manuscript of a paper (excluding figures and possibly
 the tables) output as standard ASCII text.

### <a name="_publ_requested_category"></a>\_publ\_requested\_category

The category of paper submitted. For submission to Acta
 Crystallographica Section C or Acta Crystallographica
 Section E, ONLY those codes indicated for use with those
 journals should be used.

Values:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>FA</td><td>Full article</td></tr>
  <tr><td>FI</td><td>Full submission - inorganic (Acta C)</td></tr>
  <tr><td>FO</td><td>Full submission - organic (Acta C)</td></tr>
  <tr><td>FM</td><td>Full submission - metal-organic (Acta C)</td></tr>
  <tr><td>CI</td><td>CIF-access paper - inorganic (Acta C) (no longer in use)</td></tr>
  <tr><td>CO</td><td>CIF-access paper - organic (Acta C)  (no longer in use)</td></tr>
  <tr><td>CM</td><td>CIF-access paper - metal-organic (Acta C) (no longer in use)</td></tr>
  <tr><td>EI</td><td>Electronic submission - inorganic (Acta E)</td></tr>
  <tr><td>EO</td><td>Electronic submission - organic (Acta E)</td></tr>
  <tr><td>EM</td><td>Electronic submission - metal-organic (Acta E)</td></tr>
  <tr><td>QI</td><td>Inorganic compounds (Acta E)</td></tr>
  <tr><td>QO</td><td>Organic compounds (Acta E)</td></tr>
  <tr><td>QM</td><td>Metal-organic compounds (Acta E)</td></tr>
  <tr><td>AD</td><td>Addenda and Errata (Acta C, Acta E)</td></tr>
  <tr><td>SC</td><td>Short communication</td></tr>
</table>
Default value: 'FA'

### <a name="_publ_requested_coeditor_name"></a>\_publ\_requested\_coeditor\_name

The name of the co-editor whom the authors would like to
 handle the submitted manuscript.

### <a name="_publ_requested_journal"></a>\_publ\_requested\_journal

The name of the journal to which the manuscript is being
 submitted.

### <a name="_publ_section_title"></a>\_publ\_section\_title

The sections of a manuscript if submitted in parts. As
 an alternative, see [\_publ\_manuscript\_text](#_publ_manuscript_text) and
 [\_publ\_manuscript\_processed](#_publ_manuscript_processed).

 The [\_publ\_section\_exptl\_prep](#_publ_section_exptl_prep), [\_publ\_section\_exptl\_refinement](#_publ_section_exptl_refinement)
 and [\_publ\_section\_exptl\_solution](#_publ_section_exptl_solution) items are preferred for
 separating the chemical preparation, refinement and structure
 solution aspects of the experimental description.

### <a name="_publ_section_title_footnote"></a>\_publ\_section\_title\_footnote

The sections of a manuscript if submitted in parts. As
 an alternative, see [\_publ\_manuscript\_text](#_publ_manuscript_text) and
 [\_publ\_manuscript\_processed](#_publ_manuscript_processed).

 The [\_publ\_section\_exptl\_prep](#_publ_section_exptl_prep), [\_publ\_section\_exptl\_refinement](#_publ_section_exptl_refinement)
 and [\_publ\_section\_exptl\_solution](#_publ_section_exptl_solution) items are preferred for
 separating the chemical preparation, refinement and structure
 solution aspects of the experimental description.

### <a name="_publ_section_synopsis"></a>\_publ\_section\_synopsis

The sections of a manuscript if submitted in parts. As
 an alternative, see [\_publ\_manuscript\_text](#_publ_manuscript_text) and
 [\_publ\_manuscript\_processed](#_publ_manuscript_processed).

 The [\_publ\_section\_exptl\_prep](#_publ_section_exptl_prep), [\_publ\_section\_exptl\_refinement](#_publ_section_exptl_refinement)
 and [\_publ\_section\_exptl\_solution](#_publ_section_exptl_solution) items are preferred for
 separating the chemical preparation, refinement and structure
 solution aspects of the experimental description.

### <a name="_publ_section_abstract"></a>\_publ\_section\_abstract

The sections of a manuscript if submitted in parts. As
 an alternative, see [\_publ\_manuscript\_text](#_publ_manuscript_text) and
 [\_publ\_manuscript\_processed](#_publ_manuscript_processed).

 The [\_publ\_section\_exptl\_prep](#_publ_section_exptl_prep), [\_publ\_section\_exptl\_refinement](#_publ_section_exptl_refinement)
 and [\_publ\_section\_exptl\_solution](#_publ_section_exptl_solution) items are preferred for
 separating the chemical preparation, refinement and structure
 solution aspects of the experimental description.

### <a name="_publ_section_comment"></a>\_publ\_section\_comment

The sections of a manuscript if submitted in parts. As
 an alternative, see [\_publ\_manuscript\_text](#_publ_manuscript_text) and
 [\_publ\_manuscript\_processed](#_publ_manuscript_processed).

 The [\_publ\_section\_exptl\_prep](#_publ_section_exptl_prep), [\_publ\_section\_exptl\_refinement](#_publ_section_exptl_refinement)
 and [\_publ\_section\_exptl\_solution](#_publ_section_exptl_solution) items are preferred for
 separating the chemical preparation, refinement and structure
 solution aspects of the experimental description.

### <a name="_publ_section_introduction"></a>\_publ\_section\_introduction

The sections of a manuscript if submitted in parts. As
 an alternative, see [\_publ\_manuscript\_text](#_publ_manuscript_text) and
 [\_publ\_manuscript\_processed](#_publ_manuscript_processed).

 The [\_publ\_section\_exptl\_prep](#_publ_section_exptl_prep), [\_publ\_section\_exptl\_refinement](#_publ_section_exptl_refinement)
 and [\_publ\_section\_exptl\_solution](#_publ_section_exptl_solution) items are preferred for
 separating the chemical preparation, refinement and structure
 solution aspects of the experimental description.

### <a name="_publ_section_experimental"></a>\_publ\_section\_experimental

The sections of a manuscript if submitted in parts. As
 an alternative, see [\_publ\_manuscript\_text](#_publ_manuscript_text) and
 [\_publ\_manuscript\_processed](#_publ_manuscript_processed).

 The [\_publ\_section\_exptl\_prep](#_publ_section_exptl_prep), [\_publ\_section\_exptl\_refinement](#_publ_section_exptl_refinement)
 and [\_publ\_section\_exptl\_solution](#_publ_section_exptl_solution) items are preferred for
 separating the chemical preparation, refinement and structure
 solution aspects of the experimental description.

### <a name="_publ_section_exptl_prep"></a>\_publ\_section\_exptl\_prep

The sections of a manuscript if submitted in parts. As
 an alternative, see [\_publ\_manuscript\_text](#_publ_manuscript_text) and
 [\_publ\_manuscript\_processed](#_publ_manuscript_processed).

 The [\_publ\_section\_exptl\_prep](#_publ_section_exptl_prep), [\_publ\_section\_exptl\_refinement](#_publ_section_exptl_refinement)
 and [\_publ\_section\_exptl\_solution](#_publ_section_exptl_solution) items are preferred for
 separating the chemical preparation, refinement and structure
 solution aspects of the experimental description.

### <a name="_publ_section_exptl_refinement"></a>\_publ\_section\_exptl\_refinement

The sections of a manuscript if submitted in parts. As
 an alternative, see [\_publ\_manuscript\_text](#_publ_manuscript_text) and
 [\_publ\_manuscript\_processed](#_publ_manuscript_processed).

 The [\_publ\_section\_exptl\_prep](#_publ_section_exptl_prep), [\_publ\_section\_exptl\_refinement](#_publ_section_exptl_refinement)
 and [\_publ\_section\_exptl\_solution](#_publ_section_exptl_solution) items are preferred for
 separating the chemical preparation, refinement and structure
 solution aspects of the experimental description.

### <a name="_publ_section_exptl_solution"></a>\_publ\_section\_exptl\_solution

The sections of a manuscript if submitted in parts. As
 an alternative, see [\_publ\_manuscript\_text](#_publ_manuscript_text) and
 [\_publ\_manuscript\_processed](#_publ_manuscript_processed).

 The [\_publ\_section\_exptl\_prep](#_publ_section_exptl_prep), [\_publ\_section\_exptl\_refinement](#_publ_section_exptl_refinement)
 and [\_publ\_section\_exptl\_solution](#_publ_section_exptl_solution) items are preferred for
 separating the chemical preparation, refinement and structure
 solution aspects of the experimental description.

### <a name="_publ_section_discussion"></a>\_publ\_section\_discussion

The sections of a manuscript if submitted in parts. As
 an alternative, see [\_publ\_manuscript\_text](#_publ_manuscript_text) and
 [\_publ\_manuscript\_processed](#_publ_manuscript_processed).

 The [\_publ\_section\_exptl\_prep](#_publ_section_exptl_prep), [\_publ\_section\_exptl\_refinement](#_publ_section_exptl_refinement)
 and [\_publ\_section\_exptl\_solution](#_publ_section_exptl_solution) items are preferred for
 separating the chemical preparation, refinement and structure
 solution aspects of the experimental description.

### <a name="_publ_section_acknowledgements"></a>\_publ\_section\_acknowledgements

The sections of a manuscript if submitted in parts. As
 an alternative, see [\_publ\_manuscript\_text](#_publ_manuscript_text) and
 [\_publ\_manuscript\_processed](#_publ_manuscript_processed).

 The [\_publ\_section\_exptl\_prep](#_publ_section_exptl_prep), [\_publ\_section\_exptl\_refinement](#_publ_section_exptl_refinement)
 and [\_publ\_section\_exptl\_solution](#_publ_section_exptl_solution) items are preferred for
 separating the chemical preparation, refinement and structure
 solution aspects of the experimental description.

### <a name="_publ_section_references"></a>\_publ\_section\_references

The sections of a manuscript if submitted in parts. As
 an alternative, see [\_publ\_manuscript\_text](#_publ_manuscript_text) and
 [\_publ\_manuscript\_processed](#_publ_manuscript_processed).

 The [\_publ\_section\_exptl\_prep](#_publ_section_exptl_prep), [\_publ\_section\_exptl\_refinement](#_publ_section_exptl_refinement)
 and [\_publ\_section\_exptl\_solution](#_publ_section_exptl_solution) items are preferred for
 separating the chemical preparation, refinement and structure
 solution aspects of the experimental description.

### <a name="_publ_section_related_literature"></a>\_publ\_section\_related\_literature

The sections of a manuscript if submitted in parts. As
 an alternative, see [\_publ\_manuscript\_text](#_publ_manuscript_text) and
 [\_publ\_manuscript\_processed](#_publ_manuscript_processed).

 The [\_publ\_section\_exptl\_prep](#_publ_section_exptl_prep), [\_publ\_section\_exptl\_refinement](#_publ_section_exptl_refinement)
 and [\_publ\_section\_exptl\_solution](#_publ_section_exptl_solution) items are preferred for
 separating the chemical preparation, refinement and structure
 solution aspects of the experimental description.

### <a name="_publ_section_figure_captions"></a>\_publ\_section\_figure\_captions

The sections of a manuscript if submitted in parts. As
 an alternative, see [\_publ\_manuscript\_text](#_publ_manuscript_text) and
 [\_publ\_manuscript\_processed](#_publ_manuscript_processed).

 The [\_publ\_section\_exptl\_prep](#_publ_section_exptl_prep), [\_publ\_section\_exptl\_refinement](#_publ_section_exptl_refinement)
 and [\_publ\_section\_exptl\_solution](#_publ_section_exptl_solution) items are preferred for
 separating the chemical preparation, refinement and structure
 solution aspects of the experimental description.

### <a name="_publ_section_table_legends"></a>\_publ\_section\_table\_legends

The sections of a manuscript if submitted in parts. As
 an alternative, see [\_publ\_manuscript\_text](#_publ_manuscript_text) and
 [\_publ\_manuscript\_processed](#_publ_manuscript_processed).

 The [\_publ\_section\_exptl\_prep](#_publ_section_exptl_prep), [\_publ\_section\_exptl\_refinement](#_publ_section_exptl_refinement)
 and [\_publ\_section\_exptl\_solution](#_publ_section_exptl_solution) items are preferred for
 separating the chemical preparation, refinement and structure
 solution aspects of the experimental description.

### <a name="_publ_section_keywords"></a>\_publ\_section\_keywords

The sections of a manuscript if submitted in parts. As
 an alternative, see [\_publ\_manuscript\_text](#_publ_manuscript_text) and
 [\_publ\_manuscript\_processed](#_publ_manuscript_processed).

 The [\_publ\_section\_exptl\_prep](#_publ_section_exptl_prep), [\_publ\_section\_exptl\_refinement](#_publ_section_exptl_refinement)
 and [\_publ\_section\_exptl\_solution](#_publ_section_exptl_solution) items are preferred for
 separating the chemical preparation, refinement and structure
 solution aspects of the experimental description.

## <a name="PUBL_AUTHOR"></a>PUBL\_AUTHOR

Data items in the PUBL\_AUTHOR category record details of
 the authors of a manuscript submitted for publication.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
_publ_author_name
_publ_author_address

     &#39;Willis, Anthony C.&#39;
;    Research School of Chemistry
     Australian National University
     GPO Box 4
     Canberra, ACT
     Australia    2601
;
</code></pre>
  </td><td>Example 1 - based on Willis, Beckwith &amp; Tozer
            [Acta Cryst. (1991), C47, 2276-2277].
  </td></tr>
</table>
### <a name="_publ_author_address"></a>\_publ\_author\_address

The address of a publication author. If there is more than one
 author, this will be looped with [\_publ\_author\_name](#_publ_author_name).

### <a name="_publ_author_email"></a>\_publ\_author\_email

The e-mail address of a publication author. If there is more 
 than one author, this will be looped with [\_publ\_author\_name](#_publ_author_name).
 The format of e-mail addresses is given in Section 3.4, Address 
 Specification, of  Internet Message Format, RFC 2822, P. Resnick 
 (Editor), Network Standards Group, April 2001.

### <a name="_publ_author_footnote"></a>\_publ\_author\_footnote

A footnote accompanying an author&#39;s name in the list of authors
 of a paper. Typically indicates sabbatical address, additional
 affiliations or date of decease.

### <a name="_publ_author_id_iucr"></a>\_publ\_author\_id\_iucr

Identifier in the IUCr contact database of a publication
 author.  This identifier may be available from the World
 Directory of Crystallographers ([http://wdc.iucr.org](http://wdc.iucr.org)).

### <a name="_publ_author_name"></a>\_publ\_author\_name

The name of a publication author. If there are multiple authors,
 this will be looped with [\_publ\_author\_address](#_publ_author_address). The family
 name(s), followed by a comma and including any dynastic
 components, precedes the first names or initials.

## <a name="PUBL_BODY"></a>PUBL\_BODY

Data items in the PUBL\_BODY category permit the labelling of
 different text sections within the body of a paper.
 Note that these should not be used in a paper which has
 a standard format with sections tagged by specific data names
 (such as in Acta Crystallographica Section C). Typically,
 each journal will supply a list of the specific items it
 requires in its Notes for Authors.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
_publ_body_element
_publ_body_label
_publ_body_title
_publ_body_format
_publ_body_contents

     section   1         Introduction                    cif
; X-ray diffraction from a crystalline material provides
  information on the thermally and spatially averaged
  electron density in the crystal...
;
     section   2         Theory                           tex
; In the rigid-atom approximation, the dynamic electron
  density of an atom is described by the convolution
  product of the static atomic density and a probability
  density function,
  $&rho;ho_{dyn}(&beta;f r) = &rho;ho_{stat}(&beta;f r) * P(&beta;f r). &epsilon;qno(1)$
;
</code></pre>
  </td><td>Example 1 - based on a paper by R. Restori &amp; D. Schwarzenbach
            [Acta Cryst. (1996), A52, 369-378].
  </td></tr>
  <tr><td>
<pre><code>
loop_
_publ_body_element
_publ_body_label
_publ_body_title
_publ_body_contents

     section     3
; The two-channel method for retrieval of the deformation
  electron density
;
     .
     subsection  3.1  &#39;The two-channel entropy S[&Delta;&rho;(r)]&#39;
; As the wide dynamic range involved in the total electron
  density...
;
     subsection  3.2
&#39;Uniform vs informative prior model densities&#39;        .
     subsubsection  3.2.1  &#39;Use of uniform models&#39;
; Straightforward algebra leads to expressions analogous
  to...
;
</code></pre>
  </td><td>Example 2 - based on a paper by R. J. Papoular, Y. Vekhter &amp; P. Coppens
            [Acta Cryst. (1996), A52, 397-407].
  </td></tr>
</table>
### <a name="_publ_body_contents"></a>\_publ\_body\_contents

A text section of a paper.

### <a name="_publ_body_element"></a>\_publ\_body\_element

The functional role of the associated text section.

Values:

* section
* subsection
* subsubsection
* appendix
* footnote

### <a name="_publ_body_format"></a>\_publ\_body\_format

Code indicating the appropriate typesetting conventions
 for accented characters and special symbols in the text
 section.

Values:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>ascii</td><td>no coding for special symbols</td></tr>
  <tr><td>cif</td><td>CIF convention</td></tr>
  <tr><td>latex</td><td>LaTeX</td></tr>
  <tr><td>rtf</td><td>Rich Text Format</td></tr>
  <tr><td>sgml</td><td>SGML (ISO 8879)</td></tr>
  <tr><td>tex</td><td>TeX</td></tr>
  <tr><td>troff</td><td>troff or nroff</td></tr>
</table>
Default value: 'cif'

### <a name="_publ_body_label"></a>\_publ\_body\_label

Code identifying the section of text. The combination of this
 with [\_publ\_body\_element](#_publ_body_element) must be unique.

### <a name="_publ_body_title"></a>\_publ\_body\_title

Title of the associated section of text.

## <a name="PUBL_MANUSCRIPT_INCL"></a>PUBL\_MANUSCRIPT\_INCL

Data items in the PUBL\_MANUSCRIPT\_INCL category allow
 the authors of a manuscript submitted for publication to list
 data names that should be added to the standard request list
 used by the journal printing software. Although these fields are
 primarily intended to identify CIF data items that the author
 wishes to include in a published paper, they can also be used
 to identify data names created so that non-CIF items can be
 included in the publication. Note that \*\_item names MUST be
 enclosed in single quotes.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
_publ_manuscript_incl_extra_item
_publ_manuscript_incl_extra_info
_publ_manuscript_incl_extra_defn
#
# Include Hydrogen Bonding Geometry Description
# =============================================
# Name                             explanation    standard?
# &mdash;-                             &mdash;&mdash;&mdash;&ndash;    &mdash;&mdash;&mdash;
  &#39;_geom_hbond_atom_site_label_D&#39;  &#39;H-bond donor&#39;     yes
  &#39;_geom_hbond_atom_site_label_H&#39;  &#39;H-bond hydrogen&#39;  yes
  &#39;_geom_hbond_atom_site_label_A&#39;  &#39;H-bond acceptor&#39;  yes
  &#39;_geom_hbond_distance_DH&#39;        &#39;H-bond D-H&#39;       yes
  &#39;_geom_hbond_distance_HA&#39;        &#39;H-bond H...A&#39;     yes
  &#39;_geom_hbond_distance_DA&#39;        &#39;H-bond D...A&#39;     yes
  &#39;_geom_hbond_angle_DHA&#39;          &#39;H-bond D-H...A&#39;   yes

</code></pre>
  </td><td>Example 1 - directive to include a hydrogen-bonding table, including
            cosmetic headings in comments.
  </td></tr>
  <tr><td>
<pre><code>
loop_
_publ_manuscript_incl_extra_item
_publ_manuscript_incl_extra_info
_publ_manuscript_incl_extra_defn
  &#39;_atom_site_symmetry_multiplicity&#39;
                     &#39;to emphasise special sites&#39;      yes
  &#39;_chemical_compound_source&#39;
                     &#39;rare material, unusual source&#39;   yes
  &#39;_reflns_d_resolution_high&#39;
                     &#39;limited data is a problem here&#39;  yes
  &#39;_crystal_magnetic_permeability&#39;
                     &#39;unusual value for this material&#39;  no
</code></pre>
  </td><td>Example 2 - hypothetical example including both standard CIF data items
            and a non-CIF quantity which the author wishes to list.
  </td></tr>
</table>
### <a name="_publ_manuscript_incl_extra_defn"></a>\_publ\_manuscript\_incl\_extra\_defn

Flags whether the corresponding data item marked for inclusion
 in a journal request list is a standard CIF definition or not.

Values:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>no</td><td>not a standard CIF data name</td></tr>
  <tr><td>n</td><td>abbreviation for &quot;no&quot;</td></tr>
  <tr><td>yes</td><td>a standard CIF data name</td></tr>
  <tr><td>y</td><td>abbreviation for &quot;yes&quot;</td></tr>
</table>
Default value: 'yes'

### <a name="_publ_manuscript_incl_extra_info"></a>\_publ\_manuscript\_incl\_extra\_info

A short note indicating the reason why the author wishes the
 corresponding data item marked for inclusion in the journal
 request list to be published.

### <a name="_publ_manuscript_incl_extra_item"></a>\_publ\_manuscript\_incl\_extra\_item

Specifies the inclusion of specific data into a manuscript
 which are not normally requested by the journal. The values
 of this item are the extra data names (which MUST be enclosed
 in single quotes) that will be added to the journal request list.

## <a name="REFINE"></a>REFINE

Data items in the REFINE category record details about the
 structure-refinement parameters.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
_refine_special_details     sfls:_F_calc_weight_full_matrix

_refine_ls_structure_factor_coef   F
_refine_ls_matrix_type             full
_refine_ls_weighting_scheme        calc
_refine_ls_weighting_details      &#39;w=1/(u^2^(F)+0.0004F^2^)&#39;
_refine_ls_hydrogen_treatment      refxyz
_refine_ls_extinction_method       Zachariasen
_refine_ls_extinction_coef         3514(42)
_refine_ls_extinction_expression
; Larson, A. C. (1970). &quot;Crystallographic Computing&quot;, edited
  by F. R. Ahmed. Eq. (22) p. 292. Copenhagen: Munksgaard.
;
_refine_ls_abs_structure_details
; The absolute configuration was assigned to agree with that
  of its precursor l-leucine at the chiral centre C3.
;
_refine_ls_number_reflns           1408
_refine_ls_number_parameters       272
_refine_ls_number_restraints       0
_refine_ls_number_constraints      0
_refine_ls_R_factor_all            .038
_refine_ls_R_factor_gt             .034
_refine_ls_wR_factor_all           .044
_refine_ls_wR_factor_gt            .042
_refine_ls_goodness_of_fit_all    1.462
_refine_ls_goodness_of_fit_gt     1.515
_refine_ls_shift/su_max            .535
_refine_ls_shift/su_mean           .044
_refine_diff_density_min          -.108
_refine_diff_density_max           .131
</code></pre>
  </td><td>Example 1 - based on data set TOZ of Willis, Beckwith &amp; Tozer
            [Acta Cryst. (1991), C47, 2276-2277].
  </td></tr>
</table>
### <a name="_refine_diff_density_max"></a>\_refine\_diff\_density\_max

The largest and smallest values and the root-mean-square
 deviation, in electrons per angstrom cubed, of the final
 difference electron density. The \*\_rms value is measured with
 respect to the arithmetic mean density and is derived from
 summations over each grid point in the asymmetric unit of
 the cell. This quantity is useful for assessing the
 significance of \*\_min and \*\_max values, and also for
 defining suitable contour levels.

Units: electrons\_per\_cubic\_angstrom

### <a name="_refine_diff_density_min"></a>\_refine\_diff\_density\_min

The largest and smallest values and the root-mean-square
 deviation, in electrons per angstrom cubed, of the final
 difference electron density. The \*\_rms value is measured with
 respect to the arithmetic mean density and is derived from
 summations over each grid point in the asymmetric unit of
 the cell. This quantity is useful for assessing the
 significance of \*\_min and \*\_max values, and also for
 defining suitable contour levels.

Units: electrons\_per\_cubic\_angstrom

### <a name="_refine_diff_density_rms"></a>\_refine\_diff\_density\_rms

The largest and smallest values and the root-mean-square
 deviation, in electrons per angstrom cubed, of the final
 difference electron density. The \*\_rms value is measured with
 respect to the arithmetic mean density and is derived from
 summations over each grid point in the asymmetric unit of
 the cell. This quantity is useful for assessing the
 significance of \*\_min and \*\_max values, and also for
 defining suitable contour levels.

Units: electrons\_per\_cubic\_angstrom

### <a name="_refine_ls_abs_structure_details"></a>\_refine\_ls\_abs\_structure\_details

The nature of the absolute structure and how it was determined.

### <a name="_refine_ls_abs_structure_Flack"></a>\_refine\_ls\_abs\_structure\_Flack

The measure of absolute structure as defined by Flack (1983).

 For centrosymmetric structures, the only permitted value, if the
 data name is present, is &#39;inapplicable&#39;, represented by &#39;.&#39; .

 For noncentrosymmetric structures, the value must lie in the
 99.97% Gaussian confidence interval  -3u =&lt; x =&lt; 1 + 3u and a
 standard uncertainty (e.s.d.) u must be supplied. The
 \_enumeration\_range of 0.0:1.0 is correctly interpreted as
 meaning (0.0 - 3u) =&lt; x =&lt; (1.0 + 3u).

 Ref: Flack, H. D. (1983). Acta Cryst. A39, 876-881.

### <a name="_refine_ls_abs_structure_Rogers"></a>\_refine\_ls\_abs\_structure\_Rogers

The measure of absolute structure as defined by Rogers (1981).

 The value must lie in the 99.97% Gaussian confidence interval
 -1 -3u =&lt; &eta; =&lt; 1 + 3u and a standard uncertainty (e.s.d.) u must
 be supplied. The \_enumeration\_range of -1.0:1.0 is correctly
 interpreted as meaning (-1.0 - 3u) =&lt; &eta; =&lt; (1.0 + 3u).

 Ref: Rogers, D. (1981). Acta Cryst. A37, 734-741.

### <a name="_refine_ls_d_res_high"></a>\_refine\_ls\_d\_res\_high

The smallest value in angstroms of the interplanar spacings
 of the reflections used in the refinement. This is called
 the highest resolution.

Units: angstroms

### <a name="_refine_ls_d_res_low"></a>\_refine\_ls\_d\_res\_low

The largest value in angstroms of the interplanar spacings
 of the reflections used in the refinement. This is called
 the lowest resolution.

Units: angstroms

### <a name="_refine_ls_extinction_coef"></a>\_refine\_ls\_extinction\_coef

The extinction coefficient used to calculate the correction
 factor applied to the structure-factor data. The nature of the
 extinction coefficient is given in the definitions of
 [\_refine\_ls\_extinction\_expression](#_refine_ls_extinction_expression) and
 [\_refine\_ls\_extinction\_method](#_refine_ls_extinction_method).

 For the &#39;Zachariasen&#39; method it is the r\* value; for the
 &#39;Becker-Coppens type 1 isotropic&#39; method it is the &#39;g&#39; value
 and for &#39;Becker-Coppens type 2 isotropic&#39; corrections it is
 the &#39;rho&#39; value. Note that the magnitude of these values is
 usually of the order of 10000.

 Ref:  Becker, P. J. &amp; Coppens, P. (1974). Acta Cryst. A30,
       129-147, 148-153.
       Zachariasen, W. H. (1967). Acta Cryst. 23, 558-564.
       Larson, A. C. (1967). Acta Cryst. 23, 664-665.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
3472(52)
  </td><td>Zachariasen coefficient r* = 0.347(5) E04
  </td></tr>
</table>
### <a name="_refine_ls_extinction_expression"></a>\_refine\_ls\_extinction\_expression

A description of or reference to the extinction-correction
 equation used to apply the data item [\_refine\_ls\_extinction\_coef](#_refine_ls_extinction_coef).
 This information must be sufficient to reproduce the
 extinction-correction factors applied to the structure factors.

### <a name="_refine_ls_extinction_method"></a>\_refine\_ls\_extinction\_method

A description of the extinction-correction method applied.
 This description should
 include information about the correction method, either
 &#39;Becker-Coppens&#39; or &#39;Zachariasen&#39;. The latter is sometimes
 referred to as the &#39;Larson&#39; method even though it employs
 Zachariasen&#39;s formula.

 The Becker-Coppens procedure is referred to as &#39;type 1&#39; when
 correcting secondary extinction dominated by the mosaic spread;
 as &#39;type 2&#39; when secondary extinction is dominated by particle
 size and includes a primary extinction component; and as &#39;mixed&#39;
 when there is a mixture of types 1 and 2.

 For the Becker-Coppens method, it is also necessary to set the
 mosaic distribution as either &#39;Gaussian&#39; or &#39;Lorentzian&#39; and
 the nature of the extinction as &#39;isotropic&#39; or &#39;anisotropic&#39;.
 Note that if either the &#39;mixed&#39; or &#39;anisotropic&#39; corrections
 are applied, the multiple coefficients cannot be contained in
 \*\_extinction\_coef and must be listed in [\_refine\_special\_details](#_refine_special_details).

 Ref:  Becker, P. J. &amp; Coppens, P. (1974). Acta Cryst. A30,
       129-147, 148-153.
       Zachariasen, W. H. (1967). Acta Cryst. 23, 558-564.
       Larson, A. C. (1967). Acta Cryst. 23, 664-665.

Default value: 'Zachariasen'

### <a name="_refine_ls_F_calc_details"></a>\_refine\_ls\_F\_calc\_details

Details concerning the evaluation of the structure
 factors using the expression given in
 [\_refine\_ls\_F\_calc\_formula](#_refine_ls_F_calc_formula).

### <a name="_refine_ls_F_calc_formula"></a>\_refine\_ls\_F\_calc\_formula

Analytical expression used to calculate the structure factors.  

### <a name="_refine_ls_F_calc_precision"></a>\_refine\_ls\_F\_calc\_precision

This item gives an estimate of the precision resulting
 from the numerical approximations made during the evaluation
 of the structure factors using the expression given in
 [\_refine\_ls\_F\_calc\_formula](#_refine_ls_F_calc_formula) following the method outlined
 in [\_refine\_ls\_F\_calc\_details](#_refine_ls_F_calc_details).  For X-ray diffraction the
 result is given in electrons.

### <a name="_refine_ls_goodness_of_fit_all"></a>\_refine\_ls\_goodness\_of\_fit\_all

The least-squares goodness-of-fit parameter S for all
 reflections after the final cycle of refinement.
 Ideally, account should be taken of parameters restrained
 in the least-squares refinement. See also
 \_refine\_ls\_restrained\_S\_ definitions.

     {  sum { w [ Y(obs) - Y(calc) ]^2^ }  }^1/2^
 S = { &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&ndash; }
     {            Nref - Nparam            }

 Y(obs)  = the observed coefficients
           (see [\_refine\_ls\_structure\_factor\_coef](#_refine_ls_structure_factor_coef))
 Y(calc) = the calculated coefficients
           (see [\_refine\_ls\_structure\_factor\_coef](#_refine_ls_structure_factor_coef))
 w       = the least-squares reflection weight
           [1/(u^2^)]
 u       = the standard uncertainty

 Nref   = the number of reflections used in the refinement
 Nparam = the number of refined parameters

 and the sum is taken over the specified reflections

### <a name="_refine_ls_goodness_of_fit_gt"></a>\_refine\_ls\_goodness\_of\_fit\_gt

The least-squares goodness-of-fit parameter S for
 significantly intense reflections (see
 [\_reflns\_threshold\_expression](#_reflns_threshold_expression)) after the final cycle of
 refinement. Ideally, account should be taken of parameters
 restrained in the least-squares refinement. See also
 \_refine\_ls\_restrained\_S\_ definitions.

     {  sum { w [ Y(obs) - Y(calc) ]^2^ }  }^1/2^
 S = { &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&ndash; }
     {            Nref - Nparam            }

 Y(obs)  = the observed coefficients
           (see [\_refine\_ls\_structure\_factor\_coef](#_refine_ls_structure_factor_coef))
 Y(calc) = the calculated coefficients
           (see [\_refine\_ls\_structure\_factor\_coef](#_refine_ls_structure_factor_coef))
 w       = the least-squares reflection weight
           [1/(u^2^)]
 u       = standard uncertainty

 Nref   = the number of reflections used in the refinement
 Nparam = the number of refined parameters

 and the sum is taken over the specified reflections

### <a name="_refine_ls_goodness_of_fit_obs"></a>\_refine\_ls\_goodness\_of\_fit\_obs

The least-squares goodness-of-fit parameter S for observed
 reflections (see [\_reflns\_observed\_criterion](#_reflns_observed_criterion)) after the final
 cycle of refinement. Ideally, account should be taken of
 parameters restrained in the least-squares refinement. See also
 \_refine\_ls\_restrained\_S\_ definitions.

     {  sum { w [ Y(obs) - Y(calc) ]^2^ }  }^1/2^
 S = { &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&ndash; }
     {            Nref - Nparam            }

 Y(obs)  = the observed coefficients
           (see [\_refine\_ls\_structure\_factor\_coef](#_refine_ls_structure_factor_coef))
 Y(calc) = the calculated coefficients
           (see [\_refine\_ls\_structure\_factor\_coef](#_refine_ls_structure_factor_coef))
 w       = the least-squares reflection weight
           [1/(u^2^)]
 u       = standard uncertainty (e.s.d.)

 Nref   = the number of reflections used in the refinement
 Nparam = the number of refined parameters

 and the sum is taken over the specified reflections

### <a name="_refine_ls_goodness_of_fit_ref"></a>\_refine\_ls\_goodness\_of\_fit\_ref

The least-squares goodness-of-fit parameter S for all
 reflections included in the refinement after the final cycle
 of refinement. Ideally, account should be taken of parameters
 restrained in the least-squares refinement. See also
 \_refine\_ls\_restrained\_S\_ definitions.

     {  sum | w | Y(obs) - Y(calc) |^2^ |  }^1/2^
 S = { &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&ndash; }
     {            Nref - Nparam            }

 Y(obs)  = the observed coefficients
           (see [\_refine\_ls\_structure\_factor\_coef](#_refine_ls_structure_factor_coef))
 Y(calc) = the calculated coefficients
           (see [\_refine\_ls\_structure\_factor\_coef](#_refine_ls_structure_factor_coef))
 w       = the least-squares reflection weight
           [1/(u^2^)]
 u       = standard uncertainty

 Nref   = the number of reflections used in the refinement
 Nparam = the number of refined parameters

 and the sum is taken over the specified reflections

### <a name="_refine_ls_hydrogen_treatment"></a>\_refine\_ls\_hydrogen\_treatment

Treatment of hydrogen atoms in the least-squares refinement.

Values:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>refall</td><td>refined all H-atom parameters</td></tr>
  <tr><td>refxyz</td><td>refined H-atom coordinates only</td></tr>
  <tr><td>refU</td><td>refined H-atom U&#39;s only</td></tr>
  <tr><td>noref</td><td>no refinement of H-atom parameters</td></tr>
  <tr><td>constr</td><td>H-atom parameters constrained</td></tr>
  <tr><td>mixed</td><td>some constrained, some independent</td></tr>
  <tr><td>undef</td><td>H-atom parameters not defined</td></tr>
</table>
Default value: 'undef'

### <a name="_refine_ls_matrix_type"></a>\_refine\_ls\_matrix\_type

Type of matrix used to accumulate the least-squares derivatives.

Values:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>full</td><td>full</td></tr>
  <tr><td>fullcycle</td><td>full with fixed elements per cycle</td></tr>
  <tr><td>atomblock</td><td>block diagonal per atom</td></tr>
  <tr><td>userblock</td><td>user-defined blocks</td></tr>
  <tr><td>diagonal</td><td>diagonal elements only</td></tr>
  <tr><td>sparse</td><td>selected elements only</td></tr>
</table>
Default value: 'full'

### <a name="_refine_ls_number_constraints"></a>\_refine\_ls\_number\_constraints

The number of constrained (non-refined or dependent) parameters
 in the least-squares process. These may be due to symmetry or any
 other constraint process (e.g. rigid-body refinement). See also
 [\_atom\_site\_constraints](#_atom_site_constraints) and [\_atom\_site\_refinement\_flags](#_atom_site_refinement_flags). A general
 description of constraints may appear in [\_refine\_special\_details](#_refine_special_details).

Default value: '0'

### <a name="_refine_ls_number_parameters"></a>\_refine\_ls\_number\_parameters

The number of parameters refined in the least-squares process.
 If possible, this number should include some contribution from
 the restrained parameters. The restrained parameters are
 distinct from the constrained parameters (where one or more
 parameters are linearly dependent on the refined value of
 another). Least-squares restraints often depend on geometry or
 energy considerations and this makes their direct contribution
 to this number, and to the goodness-of-fit calculation,
 difficult to assess.

### <a name="_refine_ls_number_reflns"></a>\_refine\_ls\_number\_reflns

The number of unique reflections contributing to the
 least-squares refinement calculation.

### <a name="_refine_ls_number_restraints"></a>\_refine\_ls\_number\_restraints

The number of restrained parameters. These are parameters which
 are not directly dependent on another refined parameter.
 Restrained parameters often involve geometry or energy
 dependencies.
 See also [\_atom\_site\_constraints](#_atom_site_constraints) and [\_atom\_site\_refinement\_flags](#_atom_site_refinement_flags).
 A general description of refinement constraints may appear in
 [\_refine\_special\_details](#_refine_special_details).

### <a name="_refine_ls_R_factor_all"></a>\_refine\_ls\_R\_factor\_all

Residual factor for all reflections satisfying the
 resolution limits established by [\_refine\_ls\_d\_res\_high](#_refine_ls_d_res_high) and
 [\_refine\_ls\_d\_res\_low](#_refine_ls_d_res_low). This is the conventional R
 factor. See also \_refine\_ls\_wR\_factor\_ definitions.

     sum | F(obs) - F(calc) |
 R = &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;
           sum | F(obs) |

 F(obs)  = the observed structure-factor amplitudes
 F(calc) = the calculated structure-factor amplitudes

 and the sum is taken over the specified reflections

### <a name="_refine_ls_R_factor_gt"></a>\_refine\_ls\_R\_factor\_gt

Residual factor for the reflections (with number given by
 [\_reflns\_number\_gt](#_reflns_number_gt)) judged significantly intense (i.e. satisfying
 the threshold specified by [\_reflns\_threshold\_expression](#_reflns_threshold_expression))
 and included in the refinement. The reflections also satisfy
 the resolution limits established by [\_refine\_ls\_d\_res\_high](#_refine_ls_d_res_high) and
 [\_refine\_ls\_d\_res\_low](#_refine_ls_d_res_low). This is the conventional R
 factor. See also \_refine\_ls\_wR\_factor\_ definitions.

     sum | F(obs) - F(calc) |
 R = &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;
           sum | F(obs) |

 F(obs)  = the observed structure-factor amplitudes
 F(calc) = the calculated structure-factor amplitudes

 and the sum is taken over the specified reflections

### <a name="_refine_ls_R_factor_obs"></a>\_refine\_ls\_R\_factor\_obs

Residual factor for the reflections classified as &#39;observed&#39;
 (see [\_reflns\_observed\_criterion](#_reflns_observed_criterion)) and included in the
 refinement. The reflections also satisfy the resolution limits
 established by [\_refine\_ls\_d\_res\_high](#_refine_ls_d_res_high) and
 [\_refine\_ls\_d\_res\_low](#_refine_ls_d_res_low). This is the conventional R
 factor. See also \_refine\_ls\_wR\_factor\_ definitions.

     sum | F(obs) - F(calc) |
 R = &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;
           sum | F(obs) |

 F(obs)  = the observed structure-factor amplitudes
 F(calc) = the calculated structure-factor amplitudes

 and the sum is taken over the specified reflections

### <a name="_refine_ls_R_Fsqd_factor"></a>\_refine\_ls\_R\_Fsqd\_factor

Residual factor R(Fsqd), calculated on the squared amplitudes
 of the observed and calculated structure factors, for
 significantly intense reflections (satisfying
 [\_reflns\_threshold\_expression](#_reflns_threshold_expression)) and included in the refinement.

 The reflections also satisfy the resolution limits established
 by [\_refine\_ls\_d\_res\_high](#_refine_ls_d_res_high) and [\_refine\_ls\_d\_res\_low](#_refine_ls_d_res_low).

            sum | F(obs)^2^ - F(calc)^2^ |
 R(Fsqd) = &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;-
                    sum F(obs)^2^

 F(obs)^2^  = squares of the observed structure-factor amplitudes
 F(calc)^2^ = squares of the calculated structure-factor
              amplitudes

 and the sum is taken over the specified reflections

### <a name="_refine_ls_R_I_factor"></a>\_refine\_ls\_R\_I\_factor

Residual factor R(I) for significantly intense reflections
 (satisfying [\_reflns\_threshold\_expression](#_reflns_threshold_expression)) and included in
 the refinement.

 This is most often calculated in Rietveld refinements against
 powder data, where it is referred to as R~B~ or R~Bragg~.

         sum | I(obs) - I(calc) |
 R(I) =  &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;
                sum | I(obs) |

 I(obs)  = the net observed intensities
 I(calc) = the net calculated intensities

 and the sum is taken over the specified reflections

### <a name="_refine_ls_restrained_S_all"></a>\_refine\_ls\_restrained\_S\_all

The least-squares goodness-of-fit parameter S&#39; for all
 reflections after the final cycle of least-squares refinement.
 This parameter explicitly includes the restraints applied in the
 least-squares process. See also \_refine\_ls\_goodness\_of\_fit\_
 definitions.

      {sum { w [ Y(obs) - Y(calc) ]^2^ }                   }^1/2^
      {         + sum~r~ { w~r~ [ P(calc) - P(targ) ]^2^ } }
 S&#39; = { &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&ndash; }
      {            N~ref~ + N~restr~ - N~param~            }

 Y(obs)   = the observed coefficients
            (see [\_refine\_ls\_structure\_factor\_coef](#_refine_ls_structure_factor_coef))
 Y(calc)  = the calculated coefficients
            (see [\_refine\_ls\_structure\_factor\_coef](#_refine_ls_structure_factor_coef))
 w        = the least-squares reflection weight
            [1/square of standard uncertainty (e.s.d.)]

 P(calc)  = the calculated restraint values
 P(targ)  = the target restraint values
 w~r~     = the restraint weight

 N~ref~   = the number of reflections used in the refinement
          (see [\_refine\_ls\_number\_reflns](#_refine_ls_number_reflns))
 N~restr~ = the number of restraints
          (see [\_refine\_ls\_number\_restraints](#_refine_ls_number_restraints))
 N~param~ = the number of refined parameters
          (see [\_refine\_ls\_number\_parameters](#_refine_ls_number_parameters))

 sum     is taken over the specified reflections
 sum~r~  is taken over the restraints

### <a name="_refine_ls_restrained_S_gt"></a>\_refine\_ls\_restrained\_S\_gt

The least-squares goodness-of-fit parameter S&#39; for
 significantly intense reflections (satisfying
 [\_reflns\_threshold\_expression](#_reflns_threshold_expression)) after the final cycle
 of least-squares refinement. This parameter explicitly includes
 the restraints applied in the least-squares process.
 See also \_refine\_ls\_goodness\_of\_fit\_ definitions.

      {sum { w [ Y(obs) - Y(calc) ]^2^ }                   }^1/2^
      {         + sum~r~ { w~r~ [ P(calc) - P(targ) ]^2^ } }
 S&#39; = { &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&ndash; }
      {            N~ref~ + N~restr~ - N~param~            }

 Y(obs)   = the observed coefficients
            (see [\_refine\_ls\_structure\_factor\_coef](#_refine_ls_structure_factor_coef))
 Y(calc)  = the calculated coefficients
            (see [\_refine\_ls\_structure\_factor\_coef](#_refine_ls_structure_factor_coef))
 w        = the least-squares reflection weight
            [1/square of standard uncertainty (e.s.d.)]

 P(calc)  = the calculated restraint values
 P(targ)  = the target restraint values
 w~r~     = the restraint weight

 N~ref~   = the number of reflections used in the refinement
          (see [\_refine\_ls\_number\_reflns](#_refine_ls_number_reflns))
 N~restr~ = the number of restraints
          (see [\_refine\_ls\_number\_restraints](#_refine_ls_number_restraints))
 N~param~ = the number of refined parameters
          (see [\_refine\_ls\_number\_parameters](#_refine_ls_number_parameters))

 sum     is taken over the specified reflections
 sum~r~  is taken over the restraints

### <a name="_refine_ls_restrained_S_obs"></a>\_refine\_ls\_restrained\_S\_obs

The least-squares goodness-of-fit parameter S&#39; for observed
 reflections after the final cycle of least-squares refinement.
 This parameter explicitly includes the restraints applied in the
 least-squares process.  See also \_refine\_ls\_goodness\_of\_fit\_
 definitions.

      {sum { w [ Y(obs) - Y(calc) ]^2^ }                   }^1/2^
      {         + sum~r~ { w~r~ [ P(calc) - P(targ) ]^2^ } }
 S&#39; = { &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&ndash; }
      {            N~ref~ + N~restr~ - N~param~            }

 Y(obs)   = the observed coefficients
            (see [\_refine\_ls\_structure\_factor\_coef](#_refine_ls_structure_factor_coef))
 Y(calc)  = the calculated coefficients
            (see [\_refine\_ls\_structure\_factor\_coef](#_refine_ls_structure_factor_coef))
 w        = the least-squares reflection weight
            [1/square of standard uncertainty (e.s.d.)]

 P(calc)  = the calculated restraint values
 P(targ)  = the target restraint values
 w~r~     = the restraint weight

 N~ref~   = the number of reflections used in the refinement
          (see [\_refine\_ls\_number\_reflns](#_refine_ls_number_reflns))
 N~restr~ = the number of restraints
          (see [\_refine\_ls\_number\_restraints](#_refine_ls_number_restraints))
 N~param~ = the number of refined parameters
          (see [\_refine\_ls\_number\_parameters](#_refine_ls_number_parameters))

 sum     is taken over the specified reflections
 sum~r~  is taken over the restraints

### <a name="_refine_ls_shift/esd_max"></a>\_refine\_ls\_shift/esd\_max

The largest ratio of the final least-squares parameter
 shift to the final standard uncertainty (s.u.,
 formerly described as estimated standard deviation, e.s.d.).

### <a name="_refine_ls_shift/esd_mean"></a>\_refine\_ls\_shift/esd\_mean

The average ratio of the final least-squares parameter
 shift to the final standard uncertainty (s.u.,
 formerly described as estimated standard deviation, e.s.d.).

### <a name="_refine_ls_shift/su_max"></a>\_refine\_ls\_shift/su\_max

The largest ratio of the final least-squares parameter
 shift to the final standard uncertainty.

### <a name="_refine_ls_shift/su_max_lt"></a>\_refine\_ls\_shift/su\_max\_lt

An upper limit for the largest ratio of the final
 least-squares parameter shift to the final
 standard uncertainty.  This item is used when the largest
 value of the shift divided by the final standard uncertainty
 is too small to measure.

### <a name="_refine_ls_shift/su_mean"></a>\_refine\_ls\_shift/su\_mean

The average ratio of the final least-squares parameter
 shift to the final standard uncertainty.

### <a name="_refine_ls_shift/su_mean_lt"></a>\_refine\_ls\_shift/su\_mean\_lt

An upper limit for the average ratio of the final
 least-squares parameter shift to the
 final standard uncertainty.  This
 item is used when the average value of the shift divided by
 the final standard uncertainty is too small to measure.

### <a name="_refine_ls_structure_factor_coef"></a>\_refine\_ls\_structure\_factor\_coef

Structure-factor coefficient |F|, F^2^ or I used in the
 least-squares refinement process.

Values:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>F</td><td>structure-factor magnitude</td></tr>
  <tr><td>Fsqd</td><td>structure factor squared</td></tr>
  <tr><td>Inet</td><td>net intensity</td></tr>
</table>
Default value: 'F'

### <a name="_refine_ls_weighting_details"></a>\_refine\_ls\_weighting\_details

A description of special aspects of the weighting scheme used
 in the least-squares refinement. Used to describe the weighting
 when the value of [\_refine\_ls\_weighting\_scheme](#_refine_ls_weighting_scheme) is specified
 as &#39;calc&#39;.

### <a name="_refine_ls_weighting_scheme"></a>\_refine\_ls\_weighting\_scheme

The weighting scheme applied in the least-squares process. The
 standard code may be followed by a description of the weight
 (but see [\_refine\_ls\_weighting\_details](#_refine_ls_weighting_details) for a preferred approach).

Values:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>sigma</td><td>based on measured s.u.&#39;s</td></tr>
  <tr><td>unit</td><td>unit or no weights applied</td></tr>
  <tr><td>calc</td><td>calculated weights applied</td></tr>
</table>
Default value: 'sigma'

### <a name="_refine_ls_wR_factor_all"></a>\_refine\_ls\_wR\_factor\_all

Weighted residual factors for all reflections.
 The reflections also satisfy the resolution limits established
 by [\_refine\_ls\_d\_res\_high](#_refine_ls_d_res_high) and [\_refine\_ls\_d\_res\_low](#_refine_ls_d_res_low).
 See also the \_refine\_ls\_R\_factor\_ definitions.

      ( sum w [ Y(obs) - Y(calc) ]^2^  )^1/2^
 wR = ( &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash; )
      (         sum w Y(obs)^2^       )

 Y(obs)  = the observed amplitude specified by
           [\_refine\_ls\_structure\_factor\_coef](#_refine_ls_structure_factor_coef)
 Y(calc) = the calculated amplitude specified by
           [\_refine\_ls\_structure\_factor\_coef](#_refine_ls_structure_factor_coef)
 w       = the least-squares weight

 and the sum is taken over the specified reflections

### <a name="_refine_ls_wR_factor_gt"></a>\_refine\_ls\_wR\_factor\_gt

Weighted residual factors for significantly intense reflections
 (satisfying [\_reflns\_threshold\_expression](#_reflns_threshold_expression)) included in the
 refinement.  The reflections also satisfy the resolution
 limits established by [\_refine\_ls\_d\_res\_high](#_refine_ls_d_res_high) and
 [\_refine\_ls\_d\_res\_low](#_refine_ls_d_res_low).  See also the \_refine\_ls\_R\_factor\_
 definitions.

      ( sum w [ Y(obs) - Y(calc) ]^2^  )^1/2^
 wR = ( &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash; )
      (         sum w Y(obs)^2^       )

 Y(obs)  = the observed amplitude specified by
           [\_refine\_ls\_structure\_factor\_coef](#_refine_ls_structure_factor_coef)
 Y(calc) = the calculated amplitude specified by
           [\_refine\_ls\_structure\_factor\_coef](#_refine_ls_structure_factor_coef)
 w       = the least-squares weight

 and the sum is taken over the specified reflections

### <a name="_refine_ls_wR_factor_obs"></a>\_refine\_ls\_wR\_factor\_obs

Weighted residual factors for the reflections classified as
 &#39;observed&#39; (see [\_reflns\_observed\_criterion](#_reflns_observed_criterion)) and included
 in the refinement.  The reflections also satisfy the resolution
 limits established by [\_refine\_ls\_d\_res\_high](#_refine_ls_d_res_high) and
 [\_refine\_ls\_d\_res\_low](#_refine_ls_d_res_low). See also the \_refine\_ls\_R\_factor\_
 definitions.

      ( sum w [ Y(obs) - Y(calc) ]^2^  )^1/2^
 wR = ( &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash; )
      (         sum w Y(obs)^2^       )

 Y(obs)  = the observed amplitude specified by
           [\_refine\_ls\_structure\_factor\_coef](#_refine_ls_structure_factor_coef)
 Y(calc) = the calculated amplitude specified by
           [\_refine\_ls\_structure\_factor\_coef](#_refine_ls_structure_factor_coef)
 w       = the least-squares weight

 and the sum is taken over the specified reflections

### <a name="_refine_ls_wR_factor_ref"></a>\_refine\_ls\_wR\_factor\_ref

Weighted residual factors for all reflections included in the
 refinement.  The reflections also satisfy the resolution
 limits established by [\_refine\_ls\_d\_res\_high](#_refine_ls_d_res_high) and
 [\_refine\_ls\_d\_res\_low](#_refine_ls_d_res_low).  See also the \_refine\_ls\_R\_factor\_
 definitions.

      ( sum w [ Y(obs) - Y(calc) ]^2^  )^1/2^
 wR = ( &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash; )
      (         sum w Y(obs)^2^       )

 Y(obs)  = the observed amplitude specified by
           [\_refine\_ls\_structure\_factor\_coef](#_refine_ls_structure_factor_coef)
 Y(calc) = the calculated amplitude specified by
           [\_refine\_ls\_structure\_factor\_coef](#_refine_ls_structure_factor_coef)
 w       = the least-squares weight

 and the sum is taken over the specified reflections

### <a name="_refine_special_details"></a>\_refine\_special\_details

Description of special aspects of the refinement process.

## <a name="REFINE_LS_CLASS"></a>REFINE\_LS\_CLASS

Data items in the REFINE\_LS\_CLASS category record details
 (for each reflection class separately) about the reflections
 used for the structure refinement.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
    _refine_ls_class_R_factor_gt
    _refine_ls_class_code
            0.057    &#39;Main&#39;
            0.074    &#39;Com&#39;
            0.064    &#39;NbRefls&#39;
            0.046    &#39;LaRefls&#39;
            0.112    &#39;Sat1&#39;
            0.177    &#39;Sat2&#39;
</code></pre>
  </td><td>Example 1 - example for a modulated structure extracted from van Smaalen
            [J. Phys. Condens. Matter (1991), 3, 1247-1263.]
  </td></tr>
</table>
### <a name="_refine_ls_class_code"></a>\_refine\_ls\_class\_code

The code identifying a certain reflection class. This code must
 match a [\_reflns\_class\_code](#_reflns_class_code).

### <a name="_refine_ls_class_d_res_high"></a>\_refine\_ls\_class\_d\_res\_high

For each reflection class, the highest resolution in angstroms
 for the reflections used in the refinement. This is
 the lowest d value in a reflection class.

Units: angstroms

### <a name="_refine_ls_class_d_res_low"></a>\_refine\_ls\_class\_d\_res\_low

For each reflection class, the lowest resolution in angstroms
 for the reflections used in the refinement. This is
 the highest d value in a reflection class.

Units: angstroms

### <a name="_refine_ls_class_R_factor_all"></a>\_refine\_ls\_class\_R\_factor\_all

For each reflection class, the residual factors for all
 reflections, and for significantly intense reflections (see
 [\_reflns\_threshold\_expression](#_reflns_threshold_expression)), included in the refinement.
 The reflections also satisfy the resolution limits established by
 [\_refine\_ls\_class\_d\_res\_high](#_refine_ls_class_d_res_high) and [\_refine\_ls\_class\_d\_res\_low](#_refine_ls_class_d_res_low).
 This is the conventional R factor.

     sum | F(obs) - F(calc) |
 R = &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;
           sum | F(obs) |

 F(obs)  = the observed structure-factor amplitudes
 F(calc) = the calculated structure-factor amplitudes

 and the sum is taken over the reflections of this class. See also
 [\_refine\_ls\_class\_wR\_factor\_all](#_refine_ls_class_wR_factor_all) definitions.

### <a name="_refine_ls_class_R_factor_gt"></a>\_refine\_ls\_class\_R\_factor\_gt

For each reflection class, the residual factors for all
 reflections, and for significantly intense reflections (see
 [\_reflns\_threshold\_expression](#_reflns_threshold_expression)), included in the refinement.
 The reflections also satisfy the resolution limits established by
 [\_refine\_ls\_class\_d\_res\_high](#_refine_ls_class_d_res_high) and [\_refine\_ls\_class\_d\_res\_low](#_refine_ls_class_d_res_low).
 This is the conventional R factor.

     sum | F(obs) - F(calc) |
 R = &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;
           sum | F(obs) |

 F(obs)  = the observed structure-factor amplitudes
 F(calc) = the calculated structure-factor amplitudes

 and the sum is taken over the reflections of this class. See also
 [\_refine\_ls\_class\_wR\_factor\_all](#_refine_ls_class_wR_factor_all) definitions.

### <a name="_refine_ls_class_R_Fsqd_factor"></a>\_refine\_ls\_class\_R\_Fsqd\_factor

For each reflection class, the residual factor R(F^2^) calculated
 on the squared amplitudes of the observed and calculated
 structure factors for the reflections judged significantly
 intense (i.e. satisfying the threshold specified by
 [\_reflns\_threshold\_expression](#_reflns_threshold_expression)) and included in the refinement.

 The reflections also satisfy the resolution limits established
 by [\_refine\_ls\_class\_d\_res\_high](#_refine_ls_class_d_res_high) and [\_refine\_ls\_class\_d\_res\_low](#_refine_ls_class_d_res_low).

            sum | F(obs)^2^ - F(calc)^2^ |
 R(Fsqd) = &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;-
                    sum F(obs)^2^

 F(obs)^2^  = squares of the observed structure-factor amplitudes
 F(calc)^2^ = squares of the calculated structure-factor
              amplitudes

 and the sum is taken over the reflections of this class.

### <a name="_refine_ls_class_R_I_factor"></a>\_refine\_ls\_class\_R\_I\_factor

For each reflection class, the residual factor R(I) for the
 reflections judged significantly intense (i.e. satisfying the
 threshold specified by [\_reflns\_threshold\_expression](#_reflns_threshold_expression)) and
 included in the refinement.

 This is most often calculated in Rietveld refinements
 against powder data, where it is referred to as R~B~ or R~Bragg~.

         sum | I(obs) - I(calc) |
 R(I) =  &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;
                sum | I(obs) |

 I(obs)  = the net observed intensities
 I(calc) = the net calculated intensities

 and the sum is taken over the reflections of this class.

### <a name="_refine_ls_class_wR_factor_all"></a>\_refine\_ls\_class\_wR\_factor\_all

For each reflection class, the weighted residual factors for all
 reflections included in the refinement. The reflections also
 satisfy the resolution limits established by
 [\_refine\_ls\_class\_d\_res\_high](#_refine_ls_class_d_res_high) and [\_refine\_ls\_class\_d\_res\_low](#_refine_ls_class_d_res_low).

      ( sum w [ Y(obs) - Y(calc) ]^2^  )^1/2^
 wR = ( &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash; )
      (         sum w Y(obs)^2^       )

 Y(obs)  = the observed amplitudes specified by
           [\_refine\_ls\_structure\_factor\_coef](#_refine_ls_structure_factor_coef)
 Y(calc) = the calculated amplitudes specified by
           [\_refine\_ls\_structure\_factor\_coef](#_refine_ls_structure_factor_coef)
 w       = the least-squares weights

 and the sum is taken over the reflections of this class. See
 also \_refine\_ls\_class\_R\_factor\_ definitions.

## <a name="REFLN"></a>REFLN

Data items in the REFLN category record details about the
 reflections used to determine the ATOM\_SITE data items.

 The REFLN data items refer to individual reflections and must
 be included in looped lists.

 The REFLNS data items specify the parameters that apply to all
 reflections. The REFLNS data items are not looped.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
 _refln_index_h
 _refln_index_k
 _refln_index_l
 _refln_F_squared_calc
 _refln_F_squared_meas
 _refln_F_squared_sigma
 _refln_include_status
   2   0   0       85.57       58.90      1.45 o
   3   0   0    15718.18    15631.06     30.40 o
   4   0   0    55613.11    49840.09     61.86 o
   5   0   0      246.85      241.86     10.02 o
   6   0   0       82.16       69.97      1.93 o
   7   0   0     1133.62      947.79     11.78 o
   8   0   0     2558.04     2453.33     20.44 o
   9   0   0      283.88      393.66      7.79 o
   10  0   0      283.70      171.98      4.26 o
</code></pre>
  </td><td>Example 1 - based on data set fetod of Todres, Yanovsky, Ermekov &amp; Struchkov
            [Acta Cryst. (1993), C49, 1352-1354].
  </td></tr>
  <tr><td>
<pre><code>
loop_
_refln_index_h
_refln_index_k
_refln_index_l
_refln_F_meas
_refln_F_calc
_refln_F_sigma
_refln_include_status
_refln_scale_group_code
    0   0   6  34.935  36.034   3.143  o  1
    0   0  12  42.599  40.855   2.131  o  1
    0   1   0  42.500  42.507   4.719  o  1
    0   1   1  59.172  57.976   4.719  o  1
    0   1   2  89.694  94.741   4.325  o  1
    0   1   3  51.743  52.241   3.850  o  1
    0   1   4   9.294  10.318   2.346  o  1
    0   1   5  41.160  39.951   3.313  o  1
    0   1   6   6.755   7.102    .895  &lt;  1
    0   1   7  30.693  31.171   2.668  o  1
    0   1   8  12.324  12.085   2.391  o  1
    0   1   9  15.348  15.122   2.239  o  1
    0   1  10  17.622  19.605   1.997  o  1
</code></pre>
  </td><td>Example 2 - based on standard test data set p6122 of the Xtal distribution
            [Hall, King &amp; Stewart (1995). Xtal3.4 User&#39;s Manual. University
            of Western Australia].
  </td></tr>
</table>
### <a name="_refln_A_calc"></a>\_refln\_A\_calc

The calculated and measured structure-factor component A
 (in electrons for X-ray diffraction).

 A =|F|cos(phase)

### <a name="_refln_A_meas"></a>\_refln\_A\_meas

The calculated and measured structure-factor component A
 (in electrons for X-ray diffraction).

 A =|F|cos(phase)

### <a name="_refln_B_calc"></a>\_refln\_B\_calc

The calculated and measured structure-factor component B
 (in electrons for X-ray diffraction).

 B =|F|sin(phase)

### <a name="_refln_B_meas"></a>\_refln\_B\_meas

The calculated and measured structure-factor component B
 (in electrons for X-ray diffraction).

 B =|F|sin(phase)

### <a name="_refln_class_code"></a>\_refln\_class\_code

The code identifying the class to which this reflection has been
 assigned. This code must match a value of [\_reflns\_class\_code](#_reflns_class_code).
 Reflections may be grouped into classes for a variety of
 purposes. For example, for modulated structures each reflection
 class may be defined by the number m=sum|m~i~|, where the m~i~
 are the integer coefficients that, in addition to h,k,l, index
 the corresponding diffraction vector in the basis defined
 for the reciprocal lattice.

### <a name="_refln_crystal_id"></a>\_refln\_crystal\_id

Code identifying each crystal if multiple crystals are used. Is
 used to link with [\_exptl\_crystal\_id](#_exptl_crystal_id) in the [\_exptl\_crystal](#_exptl_crystal)\_ list.

### <a name="_refln_d_spacing"></a>\_refln\_d\_spacing

The d spacing in angstroms for this reflection. This is related
 to the (sin theta)/lambda value by the expression
      [\_refln\_d\_spacing](#_refln_d_spacing) = 2/(\_refln\_sint/lambda)

Units: angstroms

### <a name="_refln_F_calc"></a>\_refln\_F\_calc

The calculated, measured and standard uncertainty (derived from
 measurement) of the structure factors (in electrons for
 X-ray diffraction).

### <a name="_refln_F_meas"></a>\_refln\_F\_meas

The calculated, measured and standard uncertainty (derived from
 measurement) of the structure factors (in electrons for
 X-ray diffraction).

### <a name="_refln_F_sigma"></a>\_refln\_F\_sigma

The calculated, measured and standard uncertainty (derived from
 measurement) of the structure factors (in electrons for
 X-ray diffraction).

### <a name="_refln_F_squared_calc"></a>\_refln\_F\_squared\_calc

Calculated, measured and estimated standard uncertainty (derived
 from measurement) of the squared structure factors (in electrons
 squared for X-ray diffraction).

### <a name="_refln_F_squared_meas"></a>\_refln\_F\_squared\_meas

Calculated, measured and estimated standard uncertainty (derived
 from measurement) of the squared structure factors (in electrons
 squared for X-ray diffraction).

### <a name="_refln_F_squared_sigma"></a>\_refln\_F\_squared\_sigma

Calculated, measured and estimated standard uncertainty (derived
 from measurement) of the squared structure factors (in electrons
 squared for X-ray diffraction).

### <a name="_refln_include_status"></a>\_refln\_include\_status

Classification of a reflection indicating its status with
 respect to inclusion in the refinement and the calculation
 of R factors.

Values:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>o</td><td>(lower-case letter o for &#39;observed&#39;)
 satisfies _refine_ls_d_res_high
 satisfies _refine_ls_d_res_low
 exceeds _reflns_threshold_expression</td></tr>
  <tr><td>&lt;</td><td>satisfies _refine_ls_d_res_high
 satisfies _refine_ls_d_res_low
 does not exceed
   _reflns_threshold_expression</td></tr>
  <tr><td>-</td><td>systematically absent reflection</td></tr>
  <tr><td>x</td><td>unreliable measurement &ndash; not used</td></tr>
  <tr><td>h</td><td>does not satisfy _refine_ls_d_res_high</td></tr>
  <tr><td>l</td><td>does not satisfy _refine_ls_d_res_low</td></tr>
</table>
Default value: 'o'

### <a name="_refln_index_h"></a>\_refln\_index\_h

Miller indices of the reflection. The values of the Miller
 indices in the REFLN category must correspond to the cell
 defined by the cell lengths and cell angles in the CELL category.

### <a name="_refln_index_k"></a>\_refln\_index\_k

Miller indices of the reflection. The values of the Miller
 indices in the REFLN category must correspond to the cell
 defined by the cell lengths and cell angles in the CELL category.

### <a name="_refln_index_l"></a>\_refln\_index\_l

Miller indices of the reflection. The values of the Miller
 indices in the REFLN category must correspond to the cell
 defined by the cell lengths and cell angles in the CELL category.

### <a name="_refln_intensity_calc"></a>\_refln\_intensity\_calc

The calculated, measured and standard uncertainty (derived from
 measurement) of the intensity, all in the same arbitrary units
 as [\_refln\_intensity\_meas](#_refln_intensity_meas).

### <a name="_refln_intensity_meas"></a>\_refln\_intensity\_meas

The calculated, measured and standard uncertainty (derived from
 measurement) of the intensity, all in the same arbitrary units
 as [\_refln\_intensity\_meas](#_refln_intensity_meas).

### <a name="_refln_intensity_sigma"></a>\_refln\_intensity\_sigma

The calculated, measured and standard uncertainty (derived from
 measurement) of the intensity, all in the same arbitrary units
 as [\_refln\_intensity\_meas](#_refln_intensity_meas).

### <a name="_refln_mean_path_length_tbar"></a>\_refln\_mean\_path\_length\_tbar

Mean path length in millimetres through the crystal for this
 reflection.

Units: millimetres

### <a name="_refln_observed_status"></a>\_refln\_observed\_status

Classification of a reflection indicating its status with
 respect to inclusion in the refinement and the calculation
 of R factors.

Values:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>o</td><td>satisfies _refine_ls_d_res_high
 satisfies _refine_ls_d_res_low
 observed by _reflns_observed_criterion</td></tr>
  <tr><td>&lt;</td><td>satisfies _refine_ls_d_res_high
 satisfies _refine_ls_d_res_low
 unobserved by _reflns_observed_criterion</td></tr>
  <tr><td>-</td><td>systematically absent reflection</td></tr>
  <tr><td>x</td><td>unreliable measurement &ndash; not used</td></tr>
  <tr><td>h</td><td>does not satisfy _refine_ls_d_res_high</td></tr>
  <tr><td>l</td><td>does not satisfy _refine_ls_d_res_low</td></tr>
</table>
Default value: 'o'

### <a name="_refln_phase_calc"></a>\_refln\_phase\_calc

The calculated structure-factor phase in degrees.

Units: degrees

### <a name="_refln_phase_meas"></a>\_refln\_phase\_meas

The measured structure-factor phase in degrees.

Units: degrees

### <a name="_refln_refinement_status"></a>\_refln\_refinement\_status

Status of a reflection in the structure-refinement process.

Values:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>incl</td><td>included in ls process</td></tr>
  <tr><td>excl</td><td>excluded from ls process</td></tr>
  <tr><td>extn</td><td>excluded due to extinction</td></tr>
</table>
Default value: 'incl'

### <a name="_refln_scale_group_code"></a>\_refln\_scale\_group\_code

Code identifying the structure-factor scale. This code must
 correspond to one of the [\_reflns\_scale\_group\_code](#_reflns_scale_group_code) values.

### <a name="_refln_sint/lambda"></a>\_refln\_sint/lambda

The (sin theta)/lambda value in reciprocal angstroms for this
 reflection.

Units: reciprocal\_angstroms

### <a name="_refln_symmetry_epsilon"></a>\_refln\_symmetry\_epsilon

The symmetry reinforcement factor corresponding to the number of
 times the reflection indices are generated identically from the
 space-group symmetry operations.

### <a name="_refln_symmetry_multiplicity"></a>\_refln\_symmetry\_multiplicity

The number of reflections symmetry-equivalent under the Laue
 symmetry to the present reflection. In the Laue symmetry, Friedel
 opposites (h k l and -h -k -l) are equivalent. Tables of
 symmetry-equivalent reflections are available in International
 Tables for Crystallography Volume A (2002), Chapter 10.1.

### <a name="_refln_wavelength"></a>\_refln\_wavelength

The mean wavelength in angstroms of the radiation used to measure
 this reflection. This is an important parameter for data
 collected using energy-dispersive detectors or the Laue method.

Units: angstroms

### <a name="_refln_wavelength_id"></a>\_refln\_wavelength\_id

Code identifying the wavelength in the [\_diffrn\_radiation](#_diffrn_radiation)\_ list.
 See [\_diffrn\_radiation\_wavelength\_id](#_diffrn_radiation_wavelength_id).

## <a name="REFLNS"></a>REFLNS

Data items in the REFLNS category record details about the
 reflections used to determine the ATOM\_SITE data items.

 The REFLN data items refer to individual reflections and must
 be included in looped lists.

 The REFLNS data items specify the parameters that apply to all
 reflections. The REFLNS data items are not looped.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
_reflns_limit_h_min                0
_reflns_limit_h_max                6
_reflns_limit_k_min                0
_reflns_limit_k_max                17
_reflns_limit_l_min                0
_reflns_limit_l_max                22
_reflns_number_total               1592
_reflns_number_gt                  1408
_reflns_threshold_expression       &#39;F &gt; 6.0u(F)&#39;
_reflns_d_resolution_high          0.8733
_reflns_d_resolution_low           11.9202
</code></pre>
  </td><td>Example 1 - based on data set TOZ of Willis, Beckwith &amp; Tozer
            [Acta Cryst. (1991), C47, 2276-2277].
  </td></tr>
</table>
### <a name="_reflns_d_resolution_high"></a>\_reflns\_d\_resolution\_high

The highest and lowest resolution in angstroms for the
 reflections. These are the smallest and largest d values.

Units: angstroms

### <a name="_reflns_d_resolution_low"></a>\_reflns\_d\_resolution\_low

The highest and lowest resolution in angstroms for the
 reflections. These are the smallest and largest d values.

Units: angstroms

### <a name="_reflns_Friedel_coverage"></a>\_reflns\_Friedel\_coverage

The proportion of Friedel-related reflections present in
 the number of &#39;independent&#39; reflections specified by
 the item [\_reflns\_number\_total](#_reflns_number_total).

 This proportion is calculated as the ratio:

   [N(crystal class) - N(Laue symmetry)] / N(Laue symmetry)

 where, working from the [\_diffrn\_refln](#_diffrn_refln)\_ list,

 N(crystal class) is the number of reflections obtained on
    averaging under the symmetry of the crystal class
 N(Laue symmetry) is the number of reflections obtained on
    averaging under the Laue symmetry.

 Examples:
   (a) For centrosymmetric structures, [\_reflns\_Friedel\_coverage](#_reflns_Friedel_coverage)
       is necessarily equal to 0.0 as the crystal class
       is identical to the Laue symmetry.
   (b) For whole-sphere data for a crystal in the space
       group P1, [\_reflns\_Friedel\_coverage](#_reflns_Friedel_coverage) is equal to 1.0,
       as no reflection h k l is equivalent to -h -k -l
       in the crystal class and all Friedel pairs
       {h k l; -h -k -l} have been measured.
   (c) For whole-sphere data in space group Pmm2,
       [\_reflns\_Friedel\_coverage](#_reflns_Friedel_coverage) will be &lt; 1.0 because
       although reflections h k l and
       -h -k -l are not equivalent when h k l indices are
       nonzero, they are when l=0.
   (d) For a crystal in the space group Pmm2, measurements of the
       two inequivalent octants h &gt;= 0, k &gt;=0, l lead to the
       same value as in (c), whereas measurements of the
       two equivalent octants h &gt;= 0, k, l &gt;= 0 will lead to
       a value of zero for [\_reflns\_Friedel\_coverage](#_reflns_Friedel_coverage).

### <a name="_reflns_limit_h_max"></a>\_reflns\_limit\_h\_max

Miller indices limits for the reported reflections. These need
 not be the same as the \_diffrn\_reflns\_limit\_ values.

### <a name="_reflns_limit_h_min"></a>\_reflns\_limit\_h\_min

Miller indices limits for the reported reflections. These need
 not be the same as the \_diffrn\_reflns\_limit\_ values.

### <a name="_reflns_limit_k_max"></a>\_reflns\_limit\_k\_max

Miller indices limits for the reported reflections. These need
 not be the same as the \_diffrn\_reflns\_limit\_ values.

### <a name="_reflns_limit_k_min"></a>\_reflns\_limit\_k\_min

Miller indices limits for the reported reflections. These need
 not be the same as the \_diffrn\_reflns\_limit\_ values.

### <a name="_reflns_limit_l_max"></a>\_reflns\_limit\_l\_max

Miller indices limits for the reported reflections. These need
 not be the same as the \_diffrn\_reflns\_limit\_ values.

### <a name="_reflns_limit_l_min"></a>\_reflns\_limit\_l\_min

Miller indices limits for the reported reflections. These need
 not be the same as the \_diffrn\_reflns\_limit\_ values.

### <a name="_reflns_number_gt"></a>\_reflns\_number\_gt

The number of reflections in the [\_refln](#_refln)\_ list (not the
 [\_diffrn\_refln](#_diffrn_refln)\_ list) that are significantly intense, satisfying
 the criterion specified by [\_reflns\_threshold\_expression](#_reflns_threshold_expression). This may
 include Friedel-equivalent reflections (i.e. those which are
 symmetry-equivalent under the Laue symmetry but inequivalent
 under the crystal class) according to the nature of the
 structure and the procedures used. Special characteristics
 of the reflections included in the [\_refln](#_refln)\_ list should be given
 in the item [\_reflns\_special\_details](#_reflns_special_details).

### <a name="_reflns_number_observed"></a>\_reflns\_number\_observed

The number of &#39;observed&#39; reflections in the [\_refln](#_refln)\_ list (not
 the [\_diffrn\_refln](#_diffrn_refln)\_ list). The observed reflections satisfy the
 threshold criterion specified by [\_reflns\_threshold\_expression](#_reflns_threshold_expression)
 (or the deprecated item [\_reflns\_observed\_criterion](#_reflns_observed_criterion)). They may
 include Friedel-equivalent reflections according to the nature
 of the structure and the procedures used. Special characteristics
 of the reflections included in the [\_refln](#_refln)\_ list should be given
 in the item [\_reflns\_special\_details](#_reflns_special_details).

### <a name="_reflns_number_total"></a>\_reflns\_number\_total

The total number of reflections in the [\_refln](#_refln)\_ list (not the
  [\_diffrn\_refln](#_diffrn_refln)\_ list). This may include Friedel-equivalent
 reflections (i.e. those which are symmetry-equivalent under the
 Laue symmetry but inequivalent under the crystal class)
 according to the nature of the structure and the procedures
 used. Special characteristics of the reflections included
 in the [\_refln](#_refln)\_ list should be given in the item
 [\_reflns\_special\_details](#_reflns_special_details).

### <a name="_reflns_observed_criterion"></a>\_reflns\_observed\_criterion

The criterion used to classify a reflection as &#39;observed&#39;. This
 criterion is usually expressed in terms of a sigma(I) or sigma(F)
 threshold.

### <a name="_reflns_special_details"></a>\_reflns\_special\_details

Description of the properties of the reported reflection list
 that are not given in other data items.  In particular, this
 should include information about the averaging (or not) of
 symmetry-equivalent reflections including Friedel pairs.

### <a name="_reflns_threshold_expression"></a>\_reflns\_threshold\_expression

The threshold, usually based on multiples of u(I), u(F^2^)
 or u(F), that serves to identify significantly intense
 reflections, the number of which is given by [\_reflns\_number\_gt](#_reflns_number_gt).
 These reflections are used in the calculation of
 [\_refine\_ls\_R\_factor\_gt](#_refine_ls_R_factor_gt).

## <a name="REFLNS_CLASS"></a>REFLNS\_CLASS

Data items in the REFLNS\_CLASS category record details, for
 each reflection class, about the reflections used to determine
 the structural parameters.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
    _reflns_class_number_gt
    _reflns_class_code
           584     &#39;Main&#39;
           226     &#39;Sat1&#39;
           50      &#39;Sat2&#39;
</code></pre>
  </td><td>Example 1 - corresponding to the one-dimensional incommensurately
            modulated structure of K~2~SeO~4~.
  </td></tr>
</table>
### <a name="_reflns_class_code"></a>\_reflns\_class\_code

The code identifying a certain reflection class.

### <a name="_reflns_class_d_res_high"></a>\_reflns\_class\_d\_res\_high

For each reflection class, the highest resolution in angstroms
 for the reflections used in the refinement. This is the smallest
 d value.

Units: angstroms

### <a name="_reflns_class_d_res_low"></a>\_reflns\_class\_d\_res\_low

For each reflection class, the lowest resolution in angstroms
 for the reflections used in the refinement. This is the largest
 d value.

Units: angstroms

### <a name="_reflns_class_description"></a>\_reflns\_class\_description

Description of each reflection class.

### <a name="_reflns_class_number_gt"></a>\_reflns\_class\_number\_gt

For each reflection class, the number of significantly intense
 reflections (see [\_reflns\_threshold\_expression](#_reflns_threshold_expression)) in the [\_refln](#_refln)\_
 list (not the [\_diffrn\_refln](#_diffrn_refln)\_ list). This may include Friedel-
 equivalent reflections (i.e. those which are symmetry-equivalent
 under the Laue symmetry but inequivalent under the crystal
 class)  according to the nature of the structure and the
 procedures used. Special characteristics of the reflections
 included in the [\_refln](#_refln)\_ list should be given in the item
 [\_reflns\_special\_details](#_reflns_special_details).

### <a name="_reflns_class_number_total"></a>\_reflns\_class\_number\_total

For each reflection class, the total number of reflections
 in the [\_refln](#_refln)\_ list (not the [\_diffrn\_refln](#_diffrn_refln)\_ list). This may
 include Friedel-equivalent reflections (i.e. those which are
 symmetry-equivalent under the Laue symmetry but inequivalent
 under the crystal class) according to the nature of the
 structure and the procedures used. Special characteristics
 of the reflections included in the [\_refln](#_refln)\_ list should be given
 in the item [\_reflns\_special\_details](#_reflns_special_details).

### <a name="_reflns_class_R_factor_all"></a>\_reflns\_class\_R\_factor\_all

For each reflection class, the residual factors for all
 reflections, and for significantly intense reflections (see
 [\_reflns\_threshold\_expression](#_reflns_threshold_expression)), included in the refinement.
 The reflections also satisfy the resolution limits established by
 [\_reflns\_class\_d\_res\_high](#_reflns_class_d_res_high) and [\_reflns\_class\_d\_res\_low](#_reflns_class_d_res_low).
 This is the conventional R factor.

     sum | F(obs) - F(calc) |
 R = &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;
           sum | F(obs) |

 F(obs)  = the observed structure-factor amplitudes
 F(calc) = the calculated structure-factor amplitudes

 and the sum is taken over the reflections of this class. See also
 [\_reflns\_class\_wR\_factor\_all](#_reflns_class_wR_factor_all) definitions.

### <a name="_reflns_class_R_factor_gt"></a>\_reflns\_class\_R\_factor\_gt

For each reflection class, the residual factors for all
 reflections, and for significantly intense reflections (see
 [\_reflns\_threshold\_expression](#_reflns_threshold_expression)), included in the refinement.
 The reflections also satisfy the resolution limits established by
 [\_reflns\_class\_d\_res\_high](#_reflns_class_d_res_high) and [\_reflns\_class\_d\_res\_low](#_reflns_class_d_res_low).
 This is the conventional R factor.

     sum | F(obs) - F(calc) |
 R = &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;
           sum | F(obs) |

 F(obs)  = the observed structure-factor amplitudes
 F(calc) = the calculated structure-factor amplitudes

 and the sum is taken over the reflections of this class. See also
 [\_reflns\_class\_wR\_factor\_all](#_reflns_class_wR_factor_all) definitions.

### <a name="_reflns_class_R_Fsqd_factor"></a>\_reflns\_class\_R\_Fsqd\_factor

For each reflection class, the residual factor R(F^2^) calculated
 on the squared amplitudes of the observed and calculated
 structure factors, for the reflections judged significantly
 intense (i.e. satisfying the threshold specified by
 [\_reflns\_threshold\_expression](#_reflns_threshold_expression)) and included in the refinement.

 The reflections also satisfy the resolution limits established
 by [\_reflns\_class\_d\_res\_high](#_reflns_class_d_res_high) and [\_reflns\_class\_d\_res\_low](#_reflns_class_d_res_low).

            sum | F(obs)^2^ - F(calc)^2^ |
 R(Fsqd) = &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;-
                    sum F(obs)^2^

 F(obs)^2^  = squares of the observed structure-factor amplitudes
 F(calc)^2^ = squares of the calculated structure-factor
              amplitudes

 and the sum is taken over the reflections of this class.

### <a name="_reflns_class_R_I_factor"></a>\_reflns\_class\_R\_I\_factor

For each reflection class, the residual factor R(I) for the
 reflections judged significantly intense (i.e. satisfying the
 threshold specified by [\_reflns\_threshold\_expression](#_reflns_threshold_expression)) and
 included in the refinement.

 This is most often calculated in Rietveld refinements
 against powder data, where it is referred to as R~B~ or R~Bragg~.

         sum | I(obs) - I(calc) |
 R(I) =  &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;
                sum | I(obs) |

 I(obs)  = the net observed intensities
 I(calc) = the net calculated intensities

 and the sum is taken over the reflections of this class.

### <a name="_reflns_class_wR_factor_all"></a>\_reflns\_class\_wR\_factor\_all

For each reflection class, the weighted residual factors for all
 reflections included in the refinement. The reflections also
 satisfy the resolution limits established by
 [\_reflns\_class\_d\_res\_high](#_reflns_class_d_res_high) and [\_reflns\_class\_d\_res\_low](#_reflns_class_d_res_low).

      ( sum w [ Y(obs) - Y(calc) ]^2^  )^1/2^
 wR = ( &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash; )
      (         sum w Y(obs)^2^       )

 Y(obs)  = the observed amplitudes specified by
           [\_refine\_ls\_structure\_factor\_coef](#_refine_ls_structure_factor_coef)
 Y(calc) = the calculated amplitudes specified by
           [\_refine\_ls\_structure\_factor\_coef](#_refine_ls_structure_factor_coef)
 w       = the least-squares weights

 and the sum is taken over the reflections of this class. See
 also \_reflns\_class\_R\_factor\_ definitions.

## <a name="REFLNS_SCALE"></a>REFLNS\_SCALE

Data items in the REFLNS\_SCALE category record details about
 the structure-factor scales. They are referenced from within
 the REFLN list through [\_refln\_scale\_group\_code](#_refln_scale_group_code).

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
_reflns_scale_group_code
_reflns_scale_meas_F
  1  .895447
  2  .912743

</code></pre>
  </td><td>Example 1 - based on standard test data set p6122 of the Xtal distribution
            [Hall, King &amp; Stewart (1995). Xtal3.4 User&#39;s Manual. University
            of Western Australia].
  </td></tr>
</table>
### <a name="_reflns_scale_group_code"></a>\_reflns\_scale\_group\_code

The code identifying a scale \_reflns\_scale\_meas\_. These are
 linked to the [\_refln](#_refln)\_ list by the [\_refln\_scale\_group\_code](#_refln_scale_group_code). These
 codes need not correspond to those in the \_diffrn\_scale\_ list.

### <a name="_reflns_scale_meas_F"></a>\_reflns\_scale\_meas\_F

Scales associated with [\_reflns\_scale\_group\_code](#_reflns_scale_group_code).

### <a name="_reflns_scale_meas_F_squared"></a>\_reflns\_scale\_meas\_F\_squared

Scales associated with [\_reflns\_scale\_group\_code](#_reflns_scale_group_code).

### <a name="_reflns_scale_meas_intensity"></a>\_reflns\_scale\_meas\_intensity

Scales associated with [\_reflns\_scale\_group\_code](#_reflns_scale_group_code).

## <a name="REFLNS_SHELL"></a>REFLNS\_SHELL

Data items in the REFLNS\_SHELL category record details about
 the reflections used to determine the ATOM\_SITE data items,
 as broken down by shells of resolution.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
_reflns_shell_d_res_high
_reflns_shell_d_res_low
_reflns_shell_meanI_over_uI_gt
_reflns_shell_number_measured_gt
_reflns_shell_number_unique_gt
_reflns_shell_percent_possible_gt
_reflns_shell_Rmerge_F_gt
  31.38  3.82  69.8  9024  2540  96.8   1.98
   3.82  3.03  26.1  7413  2364  95.1   3.85
   3.03  2.65  10.5  5640  2123  86.2   6.37
   2.65  2.41   6.4  4322  1882  76.8   8.01
   2.41  2.23   4.3  3247  1714  70.4   9.86
   2.23  2.10   3.1  1140   812  33.3  13.99
</code></pre>
  </td><td>Example 1 - based on PDB entry 5HVP and laboratory records for the
            structure corresponding to PDB entry 5HVP.
  </td></tr>
</table>
### <a name="_reflns_shell_d_res_high"></a>\_reflns\_shell\_d\_res\_high

The highest resolution in angstroms for the reflections in
 this shell. This is the smallest d value.

Units: angstroms

### <a name="_reflns_shell_d_res_low"></a>\_reflns\_shell\_d\_res\_low

The lowest resolution in angstroms for the
 reflections in this shell. This is the largest d value.

Units: angstroms

### <a name="_reflns_shell_meanI_over_sigI_all"></a>\_reflns\_shell\_meanI\_over\_sigI\_all

The ratio of the mean of the intensities of all reflections
 in this shell to the mean of the standard uncertainties of the
 intensities of all reflections in the resolution shell.

### <a name="_reflns_shell_meanI_over_sigI_gt"></a>\_reflns\_shell\_meanI\_over\_sigI\_gt

The ratio of the mean of the intensities of the significantly
 intense reflections (see [\_reflns\_threshold\_expression](#_reflns_threshold_expression)) in
 this shell to the mean of the standard uncertainties of the
 intensities of the significantly intense reflections in the
 resolution shell.

### <a name="_reflns_shell_meanI_over_sigI_obs"></a>\_reflns\_shell\_meanI\_over\_sigI\_obs

The ratio of the mean of the intensities of the reflections
 classified as &#39;observed&#39; (see [\_reflns\_observed\_criterion](#_reflns_observed_criterion)) in
 this shell to the mean of the standard uncertainties of the
 intensities of the &#39;observed&#39; reflections in the resolution
 shell.

### <a name="_reflns_shell_meanI_over_uI_all"></a>\_reflns\_shell\_meanI\_over\_uI\_all

The ratio of the mean of the intensities of all reflections
 in this shell to the mean of the standard uncertainties of the
 intensities of all reflections in the resolution shell.

### <a name="_reflns_shell_meanI_over_uI_gt"></a>\_reflns\_shell\_meanI\_over\_uI\_gt

The ratio of the mean of the intensities of the significantly
 intense reflections (see [\_reflns\_threshold\_expression](#_reflns_threshold_expression)) in
 this shell to the mean of the standard uncertainties of the
 intensities of the significantly intense reflections in the
 resolution shell.

### <a name="_reflns_shell_number_measured_all"></a>\_reflns\_shell\_number\_measured\_all

The total number of reflections measured for this
 resolution shell.

### <a name="_reflns_shell_number_measured_gt"></a>\_reflns\_shell\_number\_measured\_gt

The number of significantly intense reflections
 (see [\_reflns\_threshold\_expression](#_reflns_threshold_expression)) measured for this
 resolution shell.

### <a name="_reflns_shell_number_measured_obs"></a>\_reflns\_shell\_number\_measured\_obs

The number of reflections classified as &#39;observed&#39;
 (see [\_reflns\_observed\_criterion](#_reflns_observed_criterion)) measured for this
 resolution shell.

### <a name="_reflns_shell_number_possible"></a>\_reflns\_shell\_number\_possible

The number of unique reflections it is possible to measure in
 this reflection shell.

### <a name="_reflns_shell_number_unique_all"></a>\_reflns\_shell\_number\_unique\_all

The total number of measured reflections resulting from
 merging measured symmetry-equivalent reflections for this
 resolution shell.

### <a name="_reflns_shell_number_unique_gt"></a>\_reflns\_shell\_number\_unique\_gt

The total number of significantly intense reflections
 (see [\_reflns\_threshold\_expression](#_reflns_threshold_expression)) resulting from merging
 measured symmetry-equivalent reflections for this resolution
 shell.

### <a name="_reflns_shell_number_unique_obs"></a>\_reflns\_shell\_number\_unique\_obs

The total number of reflections classified as
 &#39;observed&#39; (see [\_reflns\_observed\_criterion](#_reflns_observed_criterion)) resulting from
 merging measured symmetry-equivalent reflections for this
 resolution shell.

### <a name="_reflns_shell_percent_possible_all"></a>\_reflns\_shell\_percent\_possible\_all

The percentage of geometrically possible reflections
 represented by all reflections measured for this
 resolution shell.

### <a name="_reflns_shell_percent_possible_gt"></a>\_reflns\_shell\_percent\_possible\_gt

The percentage of geometrically possible reflections
 represented by significantly intense reflections
 (see [\_reflns\_threshold\_expression](#_reflns_threshold_expression)) measured for this
 resolution shell.

### <a name="_reflns_shell_percent_possible_obs"></a>\_reflns\_shell\_percent\_possible\_obs

The percentage of geometrically possible reflections
 represented by reflections classified as &#39;observed&#39;
 (see [\_reflns\_observed\_criterion](#_reflns_observed_criterion)) measured for this
 resolution shell.

### <a name="_reflns_shell_Rmerge_F_all"></a>\_reflns\_shell\_Rmerge\_F\_all

The value of Rmerge(F) for all reflections in a given shell.

             sum~i~ ( sum~j~ | F~j~ - &lt;F&gt; | )
 Rmerge(F) = &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&ndash;
                 sum~i~ ( sum~j~ &lt;F&gt; )

 F~j~  = the amplitude of the jth observation of reflection i
 &lt;F&gt; = the mean of the amplitudes of all observations of
        reflection i

 sum~i~ is taken over all reflections
 sum~j~ is taken over all observations of each reflection.

### <a name="_reflns_shell_Rmerge_F_gt"></a>\_reflns\_shell\_Rmerge\_F\_gt

The value of Rmerge(F) for significantly intense reflections
 (see [\_reflns\_threshold\_expression](#_reflns_threshold_expression)) in a given shell.

             sum~i~ ( sum~j~ | F~j~ - &lt;F&gt; | )
 Rmerge(F) = &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&ndash;
                 sum~i~ ( sum~j~ &lt;F&gt; )

 F~j~  = the amplitude of the jth observation of reflection i
 &lt;F&gt; = the mean of the amplitudes of all observations of
        reflection i

 sum~i~ is taken over all reflections
 sum~j~ is taken over all observations of each reflection.

### <a name="_reflns_shell_Rmerge_F_obs"></a>\_reflns\_shell\_Rmerge\_F\_obs

The value of Rmerge(F) for reflections classified as &#39;observed&#39;
 (see [\_reflns\_observed\_criterion](#_reflns_observed_criterion)) in a given shell.

             sum~i~ ( sum~j~ | F~j~ - &lt;F&gt; | )
 Rmerge(F) = &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&ndash;
                 sum~i~ ( sum~j~ &lt;F&gt; )

 F~j~  = the amplitude of the jth observation of reflection i
 &lt;F&gt; = the mean of the amplitudes of all observations of
        reflection i

 sum~i~ is taken over all reflections
 sum~j~ is taken over all observations of each reflection.

### <a name="_reflns_shell_Rmerge_I_all"></a>\_reflns\_shell\_Rmerge\_I\_all

The value of Rmerge(I) for all reflections in a given shell.

             sum~i~ ( sum~j~ | I~j~ - &lt;I&gt; | )
 Rmerge(I) = &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&ndash;
                 sum~i~ ( sum~j~ &lt;I&gt; )

 I~j~  = the intensity of the jth observation of reflection i
 &lt;I&gt; = the mean of the intensities of all observations of
        reflection i

 sum~i~ is taken over all reflections
 sum~j~ is taken over all observations of each reflection.

### <a name="_reflns_shell_Rmerge_I_gt"></a>\_reflns\_shell\_Rmerge\_I\_gt

The value of Rmerge(I) for significantly intense reflections
 (see [\_reflns\_threshold\_expression](#_reflns_threshold_expression)) in a given shell.

             sum~i~ ( sum~j~ | I~j~ - &lt;I&gt; | )
 Rmerge(I) = &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&ndash;
                 sum~i~ ( sum~j~ &lt;I&gt; )

 I~j~  = the intensity of the jth observation of reflection i
 &lt;I&gt; = the mean of the intensities of all observations of
        reflection i

 sum~i~ is taken over all reflections
 sum~j~ is taken over all observations of each reflection.

### <a name="_reflns_shell_Rmerge_I_obs"></a>\_reflns\_shell\_Rmerge\_I\_obs

The value of Rmerge(I) for reflections classified as &#39;observed&#39;
 (see [\_reflns\_observed\_criterion](#_reflns_observed_criterion)) in a given shell.

             sum~i~ ( sum~j~ | I~j~ - &lt;I&gt; | )
 Rmerge(I) = &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&ndash;
                 sum~i~ ( sum~j~ &lt;I&gt; )

 I~j~  = the intensity of the jth observation of reflection i
 &lt;I&gt; = the mean of the intensities of all observations of
        reflection i

 sum~i~ is taken over all reflections
 sum~j~ is taken over all observations of each reflection.

## <a name="SPACE_GROUP"></a>SPACE\_GROUP

Contains all the data items that refer to the space group as a
 whole, such as its name or crystal system. They may be looped,
 for example, in a list of space groups and their properties.

 Only a subset of the SPACE\_GROUP category items appear in the
 core dictionary.  The remainder are found in the symmetry CIF
 dictionary.

 Space-group types are identified by their number as given in
 International Tables for Crystallography Vol. A. Specific
 settings of the space groups can be identified either by their
 Hall symbol or by specifying their symmetry operations.

 The commonly used Hermann-Mauguin symbol determines the
 space-group type uniquely but several different Hermann-Mauguin
 symbols may refer to the same space-group type. A
 Hermann-Mauguin symbol contains information on the choice of
 the basis, but not on the choice of origin.  Different formats
 for the Hermann-Mauguin symbol are found in the symmetry CIF
 dictionary.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
_space_group_id                 1
_space_group_name_H-M_alt       &#39;C 2/c&#39;
_space_group_IT_number          15
_space_group_name_Hall          &#39;-C 2yc&#39;
_space_group_crystal_system     monoclinic
</code></pre>
  </td><td>Example 1 - the monoclinic space group No. 15 with unique axis b.
  </td></tr>
</table>
### <a name="_space_group_crystal_system"></a>\_space\_group\_crystal\_system

The name of the system of geometric crystal classes of space
 groups (crystal system) to which the space group belongs.
 Note that rhombohedral space groups belong to the
 trigonal system.

Values:

* triclinic
* monoclinic
* orthorhombic
* tetragonal
* trigonal
* hexagonal
* cubic

### <a name="_space_group_id"></a>\_space\_group\_id

This is an identifier needed if [\_space\_group](#_space_group)\_ items are looped.

### <a name="_space_group_IT_number"></a>\_space\_group\_IT\_number

The number as assigned in International Tables for
 Crystallography Vol. A, specifying the proper affine class (i.e.
 the orientation-preserving affine class) of space groups
 (crystallographic space-group type) to which the space group
 belongs.  This number defines the space-group type but not
 the coordinate system in which it is expressed.

### <a name="_space_group_name_H-M_alt"></a>\_space\_group\_name\_H-M\_alt

[\_space\_group\_name\_H-M\_alt](#_space_group_name_H-M_alt) allows any Hermann-Mauguin symbol
 to be given. The way in which this item is used is determined
 by the user and in general is not intended to be interpreted by
 computer. It may, for example, be used to give one of the
 extended Hermann-Mauguin symbols given in Table 4.3.2.1 of
 International Tables for Crystallography Vol. A (2002) or
 a Hermann-Mauguin symbol for a conventional or unconventional
 setting.

 Each component of the space-group name is separated by a
 space or an underscore. The use of a space is strongly
 recommended.  The underscore is only retained because it
 was used in older files. It should not be
 used in new CIFs. Subscripts should appear without special
 symbols. Bars should be given as negative signs before the
 numbers to which they apply.

 The commonly used Hermann-Mauguin symbol determines the space-
 group type uniquely but a given space-group type may be
 described by more than one Hermann-Mauguin symbol. The space-
 group type is best described using [\_space\_group\_IT\_number](#_space_group_IT_number).

 The Hermann-Mauguin symbol may contain information on the
 choice of basis, but not on the choice of origin. To
 define the setting uniquely, use [\_space\_group\_name\_Hall](#_space_group_name_Hall) or
 list the symmetry operations.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
   _space_group_id
   _space_group_name_H-M_alt
    1    &#39;C m c m&#39;
    2    &#39;C 2/c 2/m 21/m&#39;
    3    &#39;A m a m&#39;
</code></pre>
  </td><td>three examples for space group No. 63
  </td></tr>
</table>
### <a name="_space_group_name_Hall"></a>\_space\_group\_name\_Hall

Space-group symbol defined by Hall.

 Each component of the space-group name is separated by a
 space or an underscore.  The use of a space is strongly
 recommended.  The underscore is only retained because it
 was used in older files.  It should not be
 used in new CIFs.

 [\_space\_group\_name\_Hall](#_space_group_name_Hall) uniquely defines the space group and
 its reference to a particular coordinate system.

 Ref: Hall, S. R. (1981). Acta Cryst. A37, 517-525; erratum
      (1981), A37, 921.
      [See also International Tables for Crystallography,
      Vol. B (2001), Chapter 1.4, Appendix 1.4.2]

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
P 2c -2ac
  </td><td>equivalent to Pca21
  </td></tr>
  <tr><td>
-I 4bd 2ab 3
  </td><td>equivalent to Ia-3d
  </td></tr>
</table>
## <a name="SPACE_GROUP_SYMOP"></a>SPACE\_GROUP\_SYMOP

Contains information about the symmetry operations of the
 space group.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
 _space_group_symop_id
 _space_group_symop_operation_xyz
   1    x,y,z
   2   -x,-y,-z
   3   -x,1/2+y,1/2-z
   4    x,1/2-y,1/2+z
</code></pre>
  </td><td>Example 1 - the symmetry operations for the space group P21/c.
  </td></tr>
</table>
### <a name="_space_group_symop_id"></a>\_space\_group\_symop\_id

An arbitrary identifier that uniquely labels each symmetry
 operation in the list.

 In order for the defaults to work correctly, the identity
 operation should have [\_space\_group\_symop\_id](#_space_group_symop_id) or
 [\_symmetry\_equiv\_pos\_site\_id](#_symmetry_equiv_pos_site_id) set to 1, and
 [\_space\_group\_symop\_operation\_xyz](#_space_group_symop_operation_xyz) or
 [\_symmetry\_equiv\_pos\_as\_xyz](#_symmetry_equiv_pos_as_xyz) set to x,y,z; 
 i.e. the operation labelled 1 should be the identity
 operation.

Default value: '1'

### <a name="_space_group_symop_operation_xyz"></a>\_space\_group\_symop\_operation\_xyz

A parsable string giving one of the symmetry operations of the
 space group in algebraic form.  If W is a matrix representation
 of the rotational part of the symmetry operation defined by the
 positions and signs of x, y and z, and w is a column of
 translations defined by fractions, an equivalent position
 X&#39; is generated from a given position X by the equation

           X&#39; = WX + w

 (Note: X is used to represent bold\_italics\_x in International
 Tables for Crystallography Vol. A, Part 5)

 When a list of symmetry operations is given, it must contain
 a complete set of coordinate representatives which generates
 all the operations of the space group by the addition of
 all primitive translations of the space group. Such
 representatives are to be found as the coordinates of
 the general-equivalent position in International Tables for
 Crystallography Vol. A (2002), to which it is necessary to 
 add any centring translations shown above the 
 general-equivalent position.

 That is to say, it is necessary to list explicitly all the
 symmetry operations required to generate all the atoms in
 the unit cell defined by the setting used.

In order for the defaults to work correctly, the identity
operation should have [\_space\_group\_symop\_id](#_space_group_symop_id) or
[\_symmetry\_equiv\_pos\_site\_id](#_symmetry_equiv_pos_site_id) set to 1, and
[\_space\_group\_symop\_operation\_xyz](#_space_group_symop_operation_xyz) or
[\_symmetry\_equiv\_pos\_as\_xyz](#_symmetry_equiv_pos_as_xyz) set to x,y,z; 
i.e. the operation labelled 1 should be the identity
operation.

Default value: 'x,y,z'

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
x,1/2-y,1/2+z
  </td><td>glide reflection through the plane (x,1/4,z),
 with glide vector (1/2)c
  </td></tr>
</table>
### <a name="_space_group_symop_sg_id"></a>\_space\_group\_symop\_sg\_id

This must match a particular value of [\_space\_group\_id](#_space_group_id), allowing
 the symmetry operation to be identified with a particular space
 group.

## <a name="SYMMETRY"></a>SYMMETRY

Data items in the SYMMETRY category record details about the
 space-group symmetry.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
_symmetry_cell_setting             orthorhombic
_symmetry_space_group_name_H-M     &#39;P 21 21 21&#39;
_symmetry_space_group_name_Hall    &#39;P 2ac 2ab&#39;
</code></pre>
  </td><td>Example 1 - based on data set TOZ of Willis, Beckwith &amp; Tozer
            [Acta Cryst. (1991), C47, 2276-2277].
  </td></tr>
</table>
### <a name="_symmetry_cell_setting"></a>\_symmetry\_cell\_setting

The cell settings for this space-group symmetry.

Values:

* triclinic
* monoclinic
* orthorhombic
* tetragonal
* rhombohedral
* trigonal
* hexagonal
* cubic

### <a name="_symmetry_Int_Tables_number"></a>\_symmetry\_Int\_Tables\_number

Space-group number from International Tables for Crystallography
 Vol. A (2002).

### <a name="_symmetry_space_group_name_H-M"></a>\_symmetry\_space\_group\_name\_H-M

Hermann-Mauguin space-group symbol. Note that the Hermann-Mauguin
 symbol does not necessarily contain complete information
 about the symmetry and the space-group origin. If used, always
 supply the FULL symbol from International Tables for
 Crystallography Vol. A (2002) and indicate the origin and
 the setting if it is not implicit. If there is any doubt
 that the equivalent positions can be uniquely deduced from
 this symbol, specify the [\_symmetry\_equiv\_pos\_as\_xyz](#_symmetry_equiv_pos_as_xyz)
 or \*\_Hall data items as well. Leave spaces between
 symbols referring to different axes.


### <a name="_symmetry_space_group_name_Hall"></a>\_symmetry\_space\_group\_name\_Hall

Space-group symbol as described by Hall. This symbol gives the
 space-group setting explicitly. Leave spaces between the separate
 components of the symbol.

 Ref: Hall, S. R. (1981). Acta Cryst. A37, 517-525; erratum
 (1981), A37, 921.

## <a name="SYMMETRY_EQUIV"></a>SYMMETRY\_EQUIV

Data items in the SYMMETRY\_EQUIV category list the
 symmetry-equivalent positions for the space group.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
_symmetry_equiv_pos_as_xyz
    +x,+y,+z  1/2-x,-y,1/2+z  1/2+x,1/2-y,-z  -x,1/2+y,1/2-z
</code></pre>
  </td><td>Example 1 - based on data set TOZ of Willis, Beckwith &amp; Tozer
            [Acta Cryst. (1991), C47, 2276-2277].
  </td></tr>
  <tr><td>
<pre><code>
loop_
_symmetry_equiv_pos_site_id
_symmetry_equiv_pos_as_xyz
    1     x,y,z
    2     1/2-x,-y,1/2+z
    3     1/2+x,1/2-y,-z
    4     -x,1/2+y,1/2-z

</code></pre>
  </td><td>Example 2 - based on data set TOZ of Willis, Beckwith &amp; Tozer
            [Acta Cryst. (1991), C47, 2276-2277]. Formally, the value of
            _symmetry_equiv_pos_site_id can be any unique character string;
            it is recommended that it be assigned the sequence number of
            the list of equivalent positions for compatibility with
            older files in which it did not appear.
  </td></tr>
</table>
### <a name="_symmetry_equiv_pos_as_xyz"></a>\_symmetry\_equiv\_pos\_as\_xyz

Symmetry-equivalent position in the &#39;xyz&#39; representation. Except
 for the space group P1, these data will be repeated in a loop.
 The format of the data item is as per International Tables for
 Crystallography Vol. A. (2002). All equivalent positions should
 be entered, including those for lattice centring and a centre of
 symmetry, if present.

 In order for the defaults to work correctly, the identity
 operation should have [\_space\_group\_symop\_id](#_space_group_symop_id) or
 [\_symmetry\_equiv\_pos\_site\_id](#_symmetry_equiv_pos_site_id) set to 1, and
 [\_space\_group\_symop\_operation\_xyz](#_space_group_symop_operation_xyz) or
 [\_symmetry\_equiv\_pos\_as\_xyz](#_symmetry_equiv_pos_as_xyz) set to x,y,z; 
 i.e. the operation labelled 1 should be the identity
 operation.

Default value: 'x,y,z'

### <a name="_symmetry_equiv_pos_site_id"></a>\_symmetry\_equiv\_pos\_site\_id

A code identifying each entry in the [\_symmetry\_equiv\_pos\_as\_xyz](#_symmetry_equiv_pos_as_xyz)
 list. It is normally the sequence number of the entry in that
 list, and should be identified with the code &#39;n&#39; in
 [\_geom](#_geom)\_\*[\_symmetry](#_symmetry)\_ codes of the form &#39;n\_klm&#39;.

 In order for the defaults to work correctly, the identity
 operation should have [\_space\_group\_symop\_id](#_space_group_symop_id) or
 [\_symmetry\_equiv\_pos\_site\_id](#_symmetry_equiv_pos_site_id) set to 1, and
 [\_space\_group\_symop\_operation\_xyz](#_space_group_symop_operation_xyz) or
 [\_symmetry\_equiv\_pos\_as\_xyz](#_symmetry_equiv_pos_as_xyz) set to x,y,z; 
 i.e. the operation labelled 1 should be the identity
 operation.

Default value: '1'

## <a name="VALENCE_PARAM"></a>VALENCE\_PARAM

Data items in the VALENCE\_PARAM category define the
 parameters used for calculating bond valences from bond
 lengths.  In addition to the parameters, a pointer
 is given to the reference (in VALENCE\_REF) from which
 the bond-valence parameters were taken.

Examples:

<table>
  <tr><th>Value</th><th>Description</th></tr>
  <tr><td>
<pre><code>
loop_
_valence_param_id
_valence_param_atom_1
_valence_param_atom_1_valence
_valence_param_atom_2
_valence_param_atom_2_valence
_valence_param_Ro
_valence_param_B
_valence_param_ref_id
_valence_param_details
  1   Cu 2 O -2 1.679 0.37 a .
  2   Cu 2 O -2 1.649 0.37 j .
  3   Cu 2 N -3 1.64  0.37 m &#39;2-coordinate N&#39;
  4   Cu 2 N -3 1.76  0.37 m &#39;3-coordinate N&#39;
loop_
_valence_ref_id
_valence_ref_reference
  a  &#39;Brown &amp; Altermatt (1985), Acta Cryst. B41, 244-247&#39;
  j  &#39;Liu &amp; Thorp (1993), Inorg. Chem. 32, 4102-4205&#39;
  m  &#39;See, Krause &amp; Strub (1998), Inorg. Chem. 37, 5369-5375&#39;
</code></pre>
  </td><td>Example 1 - a bond-valence parameter list with accompanying references.
  </td></tr>
</table>
### <a name="_valence_param_atom_1"></a>\_valence\_param\_atom\_1

The element symbol of the first atom forming the bond whose
 bond-valence parameters are given in this category.

### <a name="_valence_param_atom_1_valence"></a>\_valence\_param\_atom\_1\_valence

The valence (formal charge) of the first atom whose
 bond-valence parameters are given in this category.

### <a name="_valence_param_atom_2"></a>\_valence\_param\_atom\_2

The element symbol of the second atom forming the bond whose
 bond-valence parameters are given in this category.

### <a name="_valence_param_atom_2_valence"></a>\_valence\_param\_atom\_2\_valence

The valence (formal charge) of the second atom whose
 bond-valence parameters are given in this category.

### <a name="_valence_param_B"></a>\_valence\_param\_B

The bond-valence parameter B used in the expression

       s = exp[(Ro - R)/B]

 where s is the valence of a bond of length R.

Units: angstrom

### <a name="_valence_param_details"></a>\_valence\_param\_details

Details of or comments on the bond-valence parameters.

### <a name="_valence_param_id"></a>\_valence\_param\_id

An identifier for the valence parameters of a bond between
 the given atoms.

### <a name="_valence_param_ref_id"></a>\_valence\_param\_ref\_id

An identifier which links to the reference to the source
 from which the bond-valence parameters are taken. A child
 of [\_valence\_ref\_id](#_valence_ref_id), which it must match.

### <a name="_valence_param_Ro"></a>\_valence\_param\_Ro

The bond-valence parameter Ro used in the expression

       s = exp[(Ro - R)/B]

 where s is the valence of a bond of length R.

Units: angstrom

## <a name="VALENCE_REF"></a>VALENCE\_REF

Data items in the VALENCE\_REF category list the references
 from which the bond-valence parameters have been taken.

### <a name="_valence_ref_id"></a>\_valence\_ref\_id

An identifier for items in this category. Parent of
 [\_valence\_param\_ref\_id](#_valence_param_ref_id), which must have the same value.

### <a name="_valence_ref_reference"></a>\_valence\_ref\_reference

Literature reference from which the valence parameters
 identified by [\_valence\_param\_id](#_valence_param_id) were taken.

