!--------------------------------------------------------------------------------------------------!
!   CP2K: A general program to perform molecular dynamics simulations                              !
!   Copyright (C) 2000 - 2017  CP2K developers group                                               !
!--------------------------------------------------------------------------------------------------!

! **************************************************************************************************
!> \brief orbital transformations
!> \par History
!>      Added Taylor expansion based computation of the matrix functions (01.2004)
!>      added additional rotation variables for non-equivalent occupied orbs (08.2004)
!> \author Joost VandeVondele (06.2002)
! **************************************************************************************************
MODULE qs_ot_types
   USE bibliography,                    ONLY: VandeVondele2003,&
                                              Weber2008,&
                                              cite_reference
   USE cp_blacs_env,                    ONLY: cp_blacs_env_release,&
                                              cp_blacs_env_retain,&
                                              cp_blacs_env_type
   USE cp_dbcsr_operations,             ONLY: cp_dbcsr_m_by_n_from_row_template,&
                                              cp_dbcsr_m_by_n_from_template
   USE cp_fm_struct,                    ONLY: cp_fm_struct_get,&
                                              cp_fm_struct_type
   USE cp_para_env,                     ONLY: cp_para_env_release,&
                                              cp_para_env_retain
   USE cp_para_types,                   ONLY: cp_para_env_type
   USE dbcsr_api,                       ONLY: &
        dbcsr_allocate_matrix_set, dbcsr_deallocate_matrix_set, dbcsr_init_p, dbcsr_p_type, &
        dbcsr_release_p, dbcsr_set, dbcsr_type, dbcsr_type_complex_default, &
        dbcsr_type_no_symmetry, dbcsr_type_real_8
   USE input_constants,                 ONLY: &
        cholesky_reduce, ls_2pnt, ls_3pnt, ls_gold, ls_none, ot_algo_irac, ot_algo_taylor_or_diag, &
        ot_chol_irac, ot_lwdn_irac, ot_mini_broyden, ot_mini_cg, ot_mini_diis, ot_mini_sd, &
        ot_poly_irac, ot_precond_full_all, ot_precond_full_kinetic, ot_precond_full_single, &
        ot_precond_full_single_inverse, ot_precond_none, ot_precond_s_inverse, &
        ot_precond_solver_default, ot_precond_solver_direct, ot_precond_solver_inv_chol, &
        ot_precond_solver_update
   USE input_section_types,             ONLY: section_vals_type,&
                                              section_vals_val_get
   USE kinds,                           ONLY: dp
   USE preconditioner_types,            ONLY: preconditioner_type
#include "./base/base_uses.f90"

   IMPLICIT NONE

   PRIVATE

   PUBLIC  :: qs_ot_type
   PUBLIC  :: qs_ot_settings_type
   PUBLIC  :: qs_ot_destroy
   PUBLIC  :: qs_ot_allocate
   PUBLIC  :: qs_ot_init
   PUBLIC  :: qs_ot_settings_init
   PUBLIC  :: ot_readwrite_input

   ! notice, this variable needs to be copyable !
   ! needed for spins as e.g. in qs_ot_scf      !
! **************************************************************************************************
   TYPE qs_ot_settings_type
      LOGICAL           :: do_rotation, do_ener
      LOGICAL           :: ks
      CHARACTER(LEN=4)  :: ot_method
      CHARACTER(LEN=3)  :: ot_algorithm
      CHARACTER(LEN=4)  :: line_search_method
      CHARACTER(LEN=20) :: preconditioner_name
      INTEGER           :: preconditioner_type
      INTEGER           :: cholesky_type
      CHARACTER(LEN=20) :: precond_solver_name
      INTEGER           :: precond_solver_type
      LOGICAL           :: safer_diis
      REAL(KIND=dp)   :: ds_min
      REAL(KIND=dp)   :: energy_gap
      INTEGER           :: diis_m
      REAL(KIND=dp)   :: gold_target
      REAL(KIND=dp)   :: eps_taylor ! minimum accuracy of the taylor expansion
      INTEGER           :: max_taylor ! maximum order of the taylor expansion before switching to diagonalization
      INTEGER           :: irac_degree ! this is used to control the refinement polynomial degree
      INTEGER           :: max_irac ! maximum number of iteration for the refinement
      REAL(KIND=dp)   :: eps_irac ! target accuracy for the refinement
      REAL(KIND=dp)   :: eps_irac_quick_exit
      REAL(dp)          :: eps_irac_filter_matrix
      REAL(KIND=dp)   :: eps_irac_switch
      LOGICAL           :: on_the_fly_loc
      CHARACTER(LEN=4)  :: ortho_irac
      LOGICAL           :: occupation_preconditioner, add_nondiag_energy
      REAL(KIND=dp)   :: nondiag_energy_strength
      REAL(KIND=dp)   :: broyden_beta, broyden_gamma, broyden_sigma
      REAL(KIND=dp)   :: broyden_eta, broyden_omega, broyden_sigma_decrease
      REAL(KIND=dp)   :: broyden_sigma_min
      LOGICAL           :: broyden_forget_history, broyden_adaptive_sigma
      LOGICAL           :: broyden_enable_flip
   END TYPE qs_ot_settings_type

! **************************************************************************************************
   TYPE qs_ot_type
      ! this sets the method to be used
      TYPE(qs_ot_settings_type) :: settings
      LOGICAL                   :: restricted

      ! first part of the variables, for occupied subspace invariant optimisation

      ! add a preconditioner matrix. should be symmetric and positive definite
      ! the type of this matrix might change in the future
      TYPE(preconditioner_type), POINTER :: preconditioner

      ! these will/might change during iterations

      ! OT / TOD
      TYPE(dbcsr_type), POINTER :: matrix_p
      TYPE(dbcsr_type), POINTER :: matrix_r
      TYPE(dbcsr_type), POINTER :: matrix_sinp
      TYPE(dbcsr_type), POINTER :: matrix_cosp
      TYPE(dbcsr_type), POINTER :: matrix_sinp_b
      TYPE(dbcsr_type), POINTER :: matrix_cosp_b
      TYPE(dbcsr_type), POINTER :: matrix_buf1
      TYPE(dbcsr_type), POINTER :: matrix_buf2
      TYPE(dbcsr_type), POINTER :: matrix_buf3
      TYPE(dbcsr_type), POINTER :: matrix_buf4
      TYPE(dbcsr_type), POINTER :: matrix_os
      TYPE(dbcsr_type), POINTER :: matrix_buf1_ortho
      TYPE(dbcsr_type), POINTER :: matrix_buf2_ortho

      REAL(KIND=dp), DIMENSION(:), POINTER :: evals
      REAL(KIND=dp), DIMENSION(:), POINTER :: dum

      ! matrix os valid
      LOGICAL os_valid

      ! for efficient/parallel writing to the blacs_matrix
      TYPE(cp_para_env_type), POINTER :: para_env
      TYPE(cp_blacs_env_type), POINTER :: blacs_env

      ! mo-like vectors
      TYPE(dbcsr_type), POINTER :: matrix_c0, matrix_sc0, matrix_psc0

      ! OT / IR
      TYPE(dbcsr_type), POINTER :: buf1_k_k_nosym, buf2_k_k_nosym, &
                                   buf3_k_k_nosym, buf4_k_k_nosym, &
                                   buf1_k_k_sym, buf2_k_k_sym, buf3_k_k_sym, buf4_k_k_sym, &
                                   p_k_k_sym, buf1_n_k, buf1_n_k_dp

      ! only here for the ease of programming. These will have to be supplied
      ! explicitly at all times
      TYPE(dbcsr_type), POINTER :: matrix_x, matrix_sx, matrix_gx
      TYPE(dbcsr_type), POINTER :: matrix_dx, matrix_gx_old

      LOGICAL :: use_gx_old, use_dx

      TYPE(dbcsr_p_type), DIMENSION(:), POINTER :: matrix_h_e, matrix_h_x

      REAL(KIND=dp), DIMENSION(:, :), POINTER  :: ls_diis
      REAL(KIND=dp), DIMENSION(:, :), POINTER  :: lss_diis
      REAL(KIND=dp), DIMENSION(:), POINTER  :: c_diis
      REAL(KIND=dp), DIMENSION(:), POINTER  :: c_broy
      REAL(KIND=dp), DIMENSION(:), POINTER  :: energy_h
      INTEGER, DIMENSION(:), POINTER         :: ipivot

      REAL(KIND=dp)  :: ot_pos(53), ot_energy(53), ot_grad(53) ! HARD LIMIT FOR THE LS
      INTEGER          :: line_search_left, line_search_right, line_search_mid
      INTEGER          :: line_search_count
      LOGICAL          :: line_search_might_be_done
      REAL(KIND=dp)  :: delta, gnorm, gnorm_old, etotal, gradient
      LOGICAL          :: energy_only
      INTEGER          :: diis_iter
      CHARACTER(LEN=8) :: OT_METHOD_FULL
      INTEGER          :: OT_count
      REAL(KIND=dp)  :: ds_min
      REAL(KIND=dp)  :: broyden_adaptive_sigma

      LOGICAL          :: do_taylor
      INTEGER          :: taylor_order
      REAL(KIND=dp)  :: largest_eval_upper_bound

      ! second part of the variables, if an explicit rotation is required as well
      TYPE(dbcsr_type), POINTER :: rot_mat_u ! rotation matrix
      TYPE(dbcsr_type), POINTER :: rot_mat_x ! antisymmetric matrix that parametrises rot_matrix_u
      TYPE(dbcsr_type), POINTER :: rot_mat_dedu ! derivative of the total energy wrt to u
      TYPE(dbcsr_type), POINTER :: rot_mat_chc ! for convencience, the matrix c^T H c

      TYPE(dbcsr_p_type), DIMENSION(:), POINTER :: rot_mat_h_e
      TYPE(dbcsr_p_type), DIMENSION(:), POINTER :: rot_mat_h_x
      TYPE(dbcsr_type), POINTER :: rot_mat_gx
      TYPE(dbcsr_type), POINTER :: rot_mat_gx_old
      TYPE(dbcsr_type), POINTER :: rot_mat_dx

      REAL(KIND=dp), DIMENSION(:), POINTER :: rot_mat_evals
      TYPE(dbcsr_type), POINTER :: rot_mat_evec

      ! third part of the variables, if we need to optimize orbital energies
      REAL(KIND=dp), POINTER, DIMENSION(:) :: ener_x
      REAL(KIND=dp), POINTER, DIMENSION(:) :: ener_dx
      REAL(KIND=dp), POINTER, DIMENSION(:) :: ener_gx
      REAL(KIND=dp), POINTER, DIMENSION(:) :: ener_gx_old
      REAL(KIND=dp), POINTER, DIMENSION(:, :) :: ener_h_e
      REAL(KIND=dp), POINTER, DIMENSION(:, :) :: ener_h_x
   END TYPE qs_ot_type

   CHARACTER(len=*), PARAMETER, PRIVATE :: moduleN = 'qs_ot_types'

CONTAINS

! **************************************************************************************************
!> \brief sets default values for the settings type
!> \param settings ...
!> \par History
!>      10.2004 created [Joost VandeVondele]
! **************************************************************************************************
   SUBROUTINE qs_ot_settings_init(settings)
      TYPE(qs_ot_settings_type)                          :: settings

      settings%ot_method = "CG"
      settings%ot_algorithm = "TOD"
      settings%diis_m = 7
      settings%preconditioner_name = "FULL_KINETIC"
      settings%preconditioner_type = ot_precond_full_kinetic
      settings%cholesky_type = cholesky_reduce
      settings%precond_solver_name = "CHOLESKY_INVERSE"
      settings%precond_solver_type = ot_precond_solver_inv_chol
      settings%line_search_method = "2PNT"
      settings%ds_min = 0.15_dp
      settings%safer_diis = .TRUE.
      settings%energy_gap = 0.2_dp
      settings%eps_taylor = 1.0E-16_dp
      settings%max_taylor = 4
      settings%gold_target = 0.01_dp
      settings%do_rotation = .FALSE.
      settings%do_ener = .FALSE.
      settings%irac_degree = 4
      settings%max_irac = 50
      settings%eps_irac = 1.0E-10_dp
      settings%eps_irac_quick_exit = 1.0E-5_dp
      settings%eps_irac_switch = 1.0E-2
      settings%eps_irac_filter_matrix = 0.0_dp
      settings%on_the_fly_loc = .FALSE.
      settings%ortho_irac = "CHOL"
      settings%ks = .TRUE.
      settings%occupation_preconditioner = .FALSE.
      settings%add_nondiag_energy = .FALSE.
      settings%nondiag_energy_strength = 0.0_dp
   END SUBROUTINE qs_ot_settings_init

   ! init matrices, needs c0 and sc0 so that c0*sc0=1
! **************************************************************************************************
!> \brief ...
!> \param qs_ot_env ...
! **************************************************************************************************
   SUBROUTINE qs_ot_init(qs_ot_env)
      TYPE(qs_ot_type)                                   :: qs_ot_env

      qs_ot_env%OT_energy(:) = 0.0_dp
      qs_ot_env%OT_pos(:) = 0.0_dp
      qs_ot_env%OT_grad(:) = 0.0_dp
      qs_ot_env%line_search_count = 0

      qs_ot_env%energy_only = .FALSE.
      qs_ot_env%gnorm_old = 1.0_dp
      qs_ot_env%diis_iter = 0
      qs_ot_env%ds_min = qs_ot_env%settings%ds_min
      qs_ot_env%os_valid = .FALSE.

      CALL dbcsr_set(qs_ot_env%matrix_gx, 0.0_dp)

      IF (qs_ot_env%use_dx) &
         CALL dbcsr_set(qs_ot_env%matrix_dx, 0.0_dp)

      IF (qs_ot_env%use_gx_old) &
         CALL dbcsr_set(qs_ot_env%matrix_gx_old, 0.0_dp)

      IF (qs_ot_env%settings%do_rotation) THEN
         CALL dbcsr_set(qs_ot_env%rot_mat_gx, 0.0_dp)
         IF (qs_ot_env%use_dx) &
            CALL dbcsr_set(qs_ot_env%rot_mat_dx, 0.0_dp)
         IF (qs_ot_env%use_gx_old) &
            CALL dbcsr_set(qs_ot_env%rot_mat_gx_old, 0.0_dp)
      ENDIF
      IF (qs_ot_env%settings%do_ener) THEN
         qs_ot_env%ener_gx(:) = 0.0_dp
         IF (qs_ot_env%use_dx) &
            qs_ot_env%ener_dx(:) = 0.0_dp
         IF (qs_ot_env%use_gx_old) &
            qs_ot_env%ener_gx_old(:) = 0.0_dp
      ENDIF

   END SUBROUTINE qs_ot_init

   ! allocates the data in qs_ot_env, for a calculation with fm_struct_ref
   ! ortho_k allows for specifying an additional orthogonal subspace (i.e. c will
   ! be kept orthogonal provided c0 was, used in qs_ot_eigensolver)
! **************************************************************************************************
!> \brief ...
!> \param qs_ot_env ...
!> \param matrix_s ...
!> \param fm_struct_ref ...
!> \param ortho_k ...
! **************************************************************************************************
   SUBROUTINE qs_ot_allocate(qs_ot_env, matrix_s, fm_struct_ref, ortho_k)
      TYPE(qs_ot_type)                                   :: qs_ot_env
      TYPE(dbcsr_type), POINTER                          :: matrix_s
      TYPE(cp_fm_struct_type), POINTER                   :: fm_struct_ref
      INTEGER, OPTIONAL                                  :: ortho_k

      CHARACTER(len=*), PARAMETER :: routineN = 'qs_ot_allocate', routineP = moduleN//':'//routineN

      INTEGER                                            :: i, k, m_diis, my_ortho_k, n, ncoef
      TYPE(cp_blacs_env_type), POINTER                   :: context
      TYPE(cp_para_env_type), POINTER                    :: para_env

      CALL cite_reference(VandeVondele2003)

      NULLIFY (qs_ot_env%preconditioner)
      NULLIFY (qs_ot_env%matrix_psc0)
      NULLIFY (qs_ot_env%para_env)
      NULLIFY (qs_ot_env%blacs_env)

      CALL cp_fm_struct_get(fm_struct_ref, nrow_global=n, ncol_global=k, &
                            para_env=para_env, context=context)

      qs_ot_env%para_env => para_env
      qs_ot_env%blacs_env => context
      CALL cp_para_env_retain(para_env)
      CALL cp_blacs_env_retain(context)

      IF (PRESENT(ortho_k)) THEN
         my_ortho_k = ortho_k
      ELSE
         my_ortho_k = k
      ENDIF

      m_diis = qs_ot_env%settings%diis_m

      qs_ot_env%use_gx_old = .FALSE.
      qs_ot_env%use_dx = .FALSE.

      SELECT CASE (qs_ot_env%settings%ot_method)
      CASE ("SD")
         ! nothing
      CASE ("CG")
         qs_ot_env%use_gx_old = .TRUE.
         qs_ot_env%use_dx = .TRUE.
      CASE ("DIIS", "BROY")
         IF (m_diis .LT. 1) CPABORT("m_diis less than one")
      CASE DEFAULT
         CPABORT("Unknown option")
      END SELECT

      IF (qs_ot_env%settings%ot_method .EQ. "DIIS" .OR. &
          qs_ot_env%settings%ot_method .EQ. "BROY") THEN
         ALLOCATE (qs_ot_env%ls_diis(m_diis+1, m_diis+1))
         qs_ot_env%ls_diis = 0.0_dp
         ALLOCATE (qs_ot_env%lss_diis(m_diis+1, m_diis+1))
         ALLOCATE (qs_ot_env%c_diis(m_diis+1))
         ALLOCATE (qs_ot_env%c_broy(m_diis))
         ALLOCATE (qs_ot_env%energy_h(m_diis))
         ALLOCATE (qs_ot_env%ipivot(m_diis+1))
      ENDIF

      ALLOCATE (qs_ot_env%evals(k))
      ALLOCATE (qs_ot_env%dum(k))

      NULLIFY (qs_ot_env%matrix_os)
      NULLIFY (qs_ot_env%matrix_buf1_ortho)
      NULLIFY (qs_ot_env%matrix_buf2_ortho)
      NULLIFY (qs_ot_env%matrix_p)
      NULLIFY (qs_ot_env%matrix_r)
      NULLIFY (qs_ot_env%matrix_sinp)
      NULLIFY (qs_ot_env%matrix_cosp)
      NULLIFY (qs_ot_env%matrix_sinp_b)
      NULLIFY (qs_ot_env%matrix_cosp_b)
      NULLIFY (qs_ot_env%matrix_buf1)
      NULLIFY (qs_ot_env%matrix_buf2)
      NULLIFY (qs_ot_env%matrix_buf3)
      NULLIFY (qs_ot_env%matrix_buf4)
      NULLIFY (qs_ot_env%matrix_c0)
      NULLIFY (qs_ot_env%matrix_sc0)
      NULLIFY (qs_ot_env%matrix_x)
      NULLIFY (qs_ot_env%matrix_sx)
      NULLIFY (qs_ot_env%matrix_gx)
      NULLIFY (qs_ot_env%matrix_gx_old)
      NULLIFY (qs_ot_env%matrix_dx)
      NULLIFY (qs_ot_env%buf1_k_k_nosym)
      NULLIFY (qs_ot_env%buf2_k_k_nosym)
      NULLIFY (qs_ot_env%buf3_k_k_nosym)
      NULLIFY (qs_ot_env%buf4_k_k_nosym)
      NULLIFY (qs_ot_env%buf1_k_k_sym)
      NULLIFY (qs_ot_env%buf2_k_k_sym)
      NULLIFY (qs_ot_env%buf3_k_k_sym)
      NULLIFY (qs_ot_env%buf4_k_k_sym)
      NULLIFY (qs_ot_env%buf1_n_k)
      NULLIFY (qs_ot_env%buf1_n_k_dp)
      NULLIFY (qs_ot_env%p_k_k_sym)

      ! COMMON MATRICES
      CALL dbcsr_init_p(qs_ot_env%matrix_c0)
      CALL cp_dbcsr_m_by_n_from_row_template(qs_ot_env%matrix_c0, template=matrix_s, n=k, &
                                             sym=dbcsr_type_no_symmetry)

      CALL dbcsr_init_p(qs_ot_env%matrix_sc0)
      CALL cp_dbcsr_m_by_n_from_row_template(qs_ot_env%matrix_sc0, template=matrix_s, n=my_ortho_k, &
                                             sym=dbcsr_type_no_symmetry)

      CALL dbcsr_init_p(qs_ot_env%matrix_x)
      CALL cp_dbcsr_m_by_n_from_row_template(qs_ot_env%matrix_x, template=matrix_s, n=k, &
                                             sym=dbcsr_type_no_symmetry)

      CALL dbcsr_init_p(qs_ot_env%matrix_sx)
      CALL cp_dbcsr_m_by_n_from_row_template(qs_ot_env%matrix_sx, template=matrix_s, n=k, &
                                             sym=dbcsr_type_no_symmetry)

      CALL dbcsr_init_p(qs_ot_env%matrix_gx)
      CALL cp_dbcsr_m_by_n_from_row_template(qs_ot_env%matrix_gx, template=matrix_s, n=k, &
                                             sym=dbcsr_type_no_symmetry, data_type=dbcsr_type_real_8)

      IF (qs_ot_env%use_dx) THEN
         CALL dbcsr_init_p(qs_ot_env%matrix_dx)
         CALL cp_dbcsr_m_by_n_from_row_template(qs_ot_env%matrix_dx, template=matrix_s, n=k, &
                                                sym=dbcsr_type_no_symmetry, data_type=dbcsr_type_real_8)
      ENDIF

      IF (qs_ot_env%use_gx_old) THEN
         CALL dbcsr_init_p(qs_ot_env%matrix_gx_old)
         CALL cp_dbcsr_m_by_n_from_row_template(qs_ot_env%matrix_gx_old, template=matrix_s, n=k, &
                                                sym=dbcsr_type_no_symmetry, data_type=dbcsr_type_real_8)
      ENDIF

      SELECT CASE (qs_ot_env%settings%ot_algorithm)
      CASE ("TOD")
         CALL dbcsr_init_p(qs_ot_env%matrix_p)
         CALL cp_dbcsr_m_by_n_from_template(qs_ot_env%matrix_p, template=matrix_s, m=k, n=k, &
                                            sym=dbcsr_type_no_symmetry)

         CALL dbcsr_init_p(qs_ot_env%matrix_r)
         CALL cp_dbcsr_m_by_n_from_template(qs_ot_env%matrix_r, template=matrix_s, m=k, n=k, &
                                            sym=dbcsr_type_no_symmetry)

         CALL dbcsr_init_p(qs_ot_env%matrix_sinp)
         CALL cp_dbcsr_m_by_n_from_template(qs_ot_env%matrix_sinp, template=matrix_s, m=k, n=k, &
                                            sym=dbcsr_type_no_symmetry)

         CALL dbcsr_init_p(qs_ot_env%matrix_cosp)
         CALL cp_dbcsr_m_by_n_from_template(qs_ot_env%matrix_cosp, template=matrix_s, m=k, n=k, &
                                            sym=dbcsr_type_no_symmetry)

         CALL dbcsr_init_p(qs_ot_env%matrix_sinp_b)
         CALL cp_dbcsr_m_by_n_from_template(qs_ot_env%matrix_sinp_b, template=matrix_s, m=k, n=k, &
                                            sym=dbcsr_type_no_symmetry)

         CALL dbcsr_init_p(qs_ot_env%matrix_cosp_b)
         CALL cp_dbcsr_m_by_n_from_template(qs_ot_env%matrix_cosp_b, template=matrix_s, m=k, n=k, &
                                            sym=dbcsr_type_no_symmetry)

         CALL dbcsr_init_p(qs_ot_env%matrix_buf1)
         CALL cp_dbcsr_m_by_n_from_template(qs_ot_env%matrix_buf1, template=matrix_s, m=k, n=k, &
                                            sym=dbcsr_type_no_symmetry)

         CALL dbcsr_init_p(qs_ot_env%matrix_buf2)
         CALL cp_dbcsr_m_by_n_from_template(qs_ot_env%matrix_buf2, template=matrix_s, m=k, n=k, &
                                            sym=dbcsr_type_no_symmetry)

         CALL dbcsr_init_p(qs_ot_env%matrix_buf3)
         CALL cp_dbcsr_m_by_n_from_template(qs_ot_env%matrix_buf3, template=matrix_s, m=k, n=k, &
                                            sym=dbcsr_type_no_symmetry)

         CALL dbcsr_init_p(qs_ot_env%matrix_buf4)
         CALL cp_dbcsr_m_by_n_from_template(qs_ot_env%matrix_buf4, template=matrix_s, m=k, n=k, &
                                            sym=dbcsr_type_no_symmetry)

         CALL dbcsr_init_p(qs_ot_env%matrix_os)
         CALL cp_dbcsr_m_by_n_from_template(qs_ot_env%matrix_os, template=matrix_s, m=my_ortho_k, n=my_ortho_k, &
                                            sym=dbcsr_type_no_symmetry)

         CALL dbcsr_init_p(qs_ot_env%matrix_buf1_ortho)
         CALL cp_dbcsr_m_by_n_from_template(qs_ot_env%matrix_buf1_ortho, template=matrix_s, m=my_ortho_k, n=k, &
                                            sym=dbcsr_type_no_symmetry)

         CALL dbcsr_init_p(qs_ot_env%matrix_buf2_ortho)
         CALL cp_dbcsr_m_by_n_from_template(qs_ot_env%matrix_buf2_ortho, template=matrix_s, m=my_ortho_k, n=k, &
                                            sym=dbcsr_type_no_symmetry)

      CASE ("REF")
         CALL dbcsr_init_p(qs_ot_env%buf1_k_k_nosym)
         CALL cp_dbcsr_m_by_n_from_template(qs_ot_env%buf1_k_k_nosym, template=matrix_s, m=k, n=k, &
                                            sym=dbcsr_type_no_symmetry)

         CALL dbcsr_init_p(qs_ot_env%buf2_k_k_nosym)
         CALL cp_dbcsr_m_by_n_from_template(qs_ot_env%buf2_k_k_nosym, template=matrix_s, m=k, n=k, &
                                            sym=dbcsr_type_no_symmetry)

         CALL dbcsr_init_p(qs_ot_env%buf3_k_k_nosym)
         CALL cp_dbcsr_m_by_n_from_template(qs_ot_env%buf3_k_k_nosym, template=matrix_s, m=k, n=k, &
                                            sym=dbcsr_type_no_symmetry)

         CALL dbcsr_init_p(qs_ot_env%buf4_k_k_nosym)
         CALL cp_dbcsr_m_by_n_from_template(qs_ot_env%buf4_k_k_nosym, template=matrix_s, m=k, n=k, &
                                            sym=dbcsr_type_no_symmetry)

! It claims to be symmetric but to avoid dbcsr conusion nonsymmetric is kept
         CALL dbcsr_init_p(qs_ot_env%buf1_k_k_sym)
         CALL cp_dbcsr_m_by_n_from_template(qs_ot_env%buf1_k_k_sym, template=matrix_s, m=k, n=k, &
                                            sym=dbcsr_type_no_symmetry)

         CALL dbcsr_init_p(qs_ot_env%buf2_k_k_sym)
         CALL cp_dbcsr_m_by_n_from_template(qs_ot_env%buf2_k_k_sym, template=matrix_s, m=k, n=k, &
                                            sym=dbcsr_type_no_symmetry)

         CALL dbcsr_init_p(qs_ot_env%buf3_k_k_sym)
         CALL cp_dbcsr_m_by_n_from_template(qs_ot_env%buf3_k_k_sym, template=matrix_s, m=k, n=k, &
                                            sym=dbcsr_type_no_symmetry)
         !
         CALL dbcsr_init_p(qs_ot_env%buf4_k_k_sym)
         CALL cp_dbcsr_m_by_n_from_template(qs_ot_env%buf4_k_k_sym, template=matrix_s, m=k, n=k, &
                                            sym=dbcsr_type_no_symmetry)
         !
         CALL dbcsr_init_p(qs_ot_env%p_k_k_sym)
         CALL cp_dbcsr_m_by_n_from_template(qs_ot_env%p_k_k_sym, template=matrix_s, m=k, n=k, &
                                            sym=dbcsr_type_no_symmetry)
         !
         CALL dbcsr_init_p(qs_ot_env%buf1_n_k)
         CALL cp_dbcsr_m_by_n_from_row_template(qs_ot_env%buf1_n_k, template=matrix_s, n=k, &
                                                sym=dbcsr_type_no_symmetry)
         !

      END SELECT

      IF (qs_ot_env%settings%ot_method .EQ. "DIIS" .OR. &
          qs_ot_env%settings%ot_method .EQ. "BROY") THEN
         NULLIFY (qs_ot_env%matrix_h_e)
         NULLIFY (qs_ot_env%matrix_h_x)
         CALL dbcsr_allocate_matrix_set(qs_ot_env%matrix_h_e, m_diis)
         CALL dbcsr_allocate_matrix_set(qs_ot_env%matrix_h_x, m_diis)
         DO i = 1, m_diis
            CALL dbcsr_init_p(qs_ot_env%matrix_h_x(i)%matrix)
            CALL cp_dbcsr_m_by_n_from_row_template(qs_ot_env%matrix_h_x(i)%matrix, template=matrix_s, n=k, &
                                                   sym=dbcsr_type_no_symmetry, data_type=dbcsr_type_real_8)

            CALL dbcsr_init_p(qs_ot_env%matrix_h_e(i)%matrix)
            CALL cp_dbcsr_m_by_n_from_row_template(qs_ot_env%matrix_h_e(i)%matrix, template=matrix_s, n=k, &
                                                   sym=dbcsr_type_no_symmetry, data_type=dbcsr_type_real_8)
         ENDDO
      ENDIF

      NULLIFY (qs_ot_env%rot_mat_u, qs_ot_env%rot_mat_x, qs_ot_env%rot_mat_h_e, qs_ot_env%rot_mat_h_x, &
               qs_ot_env%rot_mat_gx, qs_ot_env%rot_mat_gx_old, qs_ot_env%rot_mat_dx, &
               qs_ot_env%rot_mat_evals, qs_ot_env%rot_mat_evec, qs_ot_env%rot_mat_dedu, qs_ot_env%rot_mat_chc)

      IF (qs_ot_env%settings%do_rotation) THEN
         CALL dbcsr_init_p(qs_ot_env%rot_mat_u)
         CALL cp_dbcsr_m_by_n_from_template(qs_ot_env%rot_mat_u, template=matrix_s, m=k, n=k, &
                                            sym=dbcsr_type_no_symmetry)

         CALL dbcsr_init_p(qs_ot_env%rot_mat_x)
         CALL cp_dbcsr_m_by_n_from_template(qs_ot_env%rot_mat_x, template=matrix_s, m=k, n=k, &
                                            sym=dbcsr_type_no_symmetry)

         CALL dbcsr_init_p(qs_ot_env%rot_mat_dedu)
         CALL cp_dbcsr_m_by_n_from_template(qs_ot_env%rot_mat_dedu, template=matrix_s, m=k, n=k, &
                                            sym=dbcsr_type_no_symmetry)

         CALL dbcsr_init_p(qs_ot_env%rot_mat_chc)
         CALL cp_dbcsr_m_by_n_from_template(qs_ot_env%rot_mat_chc, template=matrix_s, m=k, n=k, &
                                            sym=dbcsr_type_no_symmetry)

         IF (qs_ot_env%settings%ot_method .EQ. "DIIS") THEN
            CALL dbcsr_allocate_matrix_set(qs_ot_env%rot_mat_h_e, m_diis)
            CALL dbcsr_allocate_matrix_set(qs_ot_env%rot_mat_h_x, m_diis)
            DO i = 1, m_diis
               CALL dbcsr_init_p(qs_ot_env%rot_mat_h_e(i)%matrix)
               CALL cp_dbcsr_m_by_n_from_template(qs_ot_env%rot_mat_h_e(i)%matrix, template=matrix_s, m=k, n=k, &
                                                  sym=dbcsr_type_no_symmetry)

               CALL dbcsr_init_p(qs_ot_env%rot_mat_h_x(i)%matrix)
               CALL cp_dbcsr_m_by_n_from_template(qs_ot_env%rot_mat_h_x(i)%matrix, template=matrix_s, m=k, n=k, &
                                                  sym=dbcsr_type_no_symmetry)
            ENDDO
         ENDIF

         ALLOCATE (qs_ot_env%rot_mat_evals(k))

         CALL dbcsr_init_p(qs_ot_env%rot_mat_evec)
         CALL cp_dbcsr_m_by_n_from_template(qs_ot_env%rot_mat_evec, template=matrix_s, m=k, n=k, &
                                            sym=dbcsr_type_no_symmetry, data_type=dbcsr_type_complex_default)

         CALL dbcsr_init_p(qs_ot_env%rot_mat_gx)
         CALL cp_dbcsr_m_by_n_from_template(qs_ot_env%rot_mat_gx, template=matrix_s, m=k, n=k, &
                                            sym=dbcsr_type_no_symmetry)

         IF (qs_ot_env%use_gx_old) THEN
            CALL dbcsr_init_p(qs_ot_env%rot_mat_gx_old)
            CALL cp_dbcsr_m_by_n_from_template(qs_ot_env%rot_mat_gx_old, template=matrix_s, m=k, n=k, &
                                               sym=dbcsr_type_no_symmetry)
         ENDIF

         IF (qs_ot_env%use_dx) THEN
            CALL dbcsr_init_p(qs_ot_env%rot_mat_dx)
            CALL cp_dbcsr_m_by_n_from_template(qs_ot_env%rot_mat_dx, template=matrix_s, m=k, n=k, &
                                               sym=dbcsr_type_no_symmetry)
         ENDIF

      ENDIF

      IF (qs_ot_env%settings%do_ener) THEN
         ncoef = k
         ALLOCATE (qs_ot_env%ener_x(ncoef))

         IF (qs_ot_env%settings%ot_method .EQ. "DIIS") THEN
            ALLOCATE (qs_ot_env%ener_h_e(m_diis, ncoef))
            ALLOCATE (qs_ot_env%ener_h_x(m_diis, ncoef))
         ENDIF

         ALLOCATE (qs_ot_env%ener_gx(ncoef))

         IF (qs_ot_env%use_gx_old) THEN
            ALLOCATE (qs_ot_env%ener_gx_old(ncoef))
         ENDIF

         IF (qs_ot_env%use_dx) THEN
            ALLOCATE (qs_ot_env%ener_dx(ncoef))
            qs_ot_env%ener_dx = 0.0_dp
         ENDIF
      ENDIF

   END SUBROUTINE qs_ot_allocate

   ! deallocates data
! **************************************************************************************************
!> \brief ...
!> \param qs_ot_env ...
! **************************************************************************************************
   SUBROUTINE qs_ot_destroy(qs_ot_env)
      TYPE(qs_ot_type)                                   :: qs_ot_env

      CHARACTER(len=*), PARAMETER :: routineN = 'qs_ot_destroy', routineP = moduleN//':'//routineN

      CALL cp_para_env_release(qs_ot_env%para_env)
      CALL cp_blacs_env_release(qs_ot_env%blacs_env)

      DEALLOCATE (qs_ot_env%evals)
      DEALLOCATE (qs_ot_env%dum)

      IF (ASSOCIATED(qs_ot_env%matrix_os)) CALL dbcsr_release_p(qs_ot_env%matrix_os)
      IF (ASSOCIATED(qs_ot_env%matrix_p)) CALL dbcsr_release_p(qs_ot_env%matrix_p)
      IF (ASSOCIATED(qs_ot_env%matrix_cosp)) CALL dbcsr_release_p(qs_ot_env%matrix_cosp)
      IF (ASSOCIATED(qs_ot_env%matrix_sinp)) CALL dbcsr_release_p(qs_ot_env%matrix_sinp)
      IF (ASSOCIATED(qs_ot_env%matrix_r)) CALL dbcsr_release_p(qs_ot_env%matrix_r)
      IF (ASSOCIATED(qs_ot_env%matrix_cosp_b)) CALL dbcsr_release_p(qs_ot_env%matrix_cosp_b)
      IF (ASSOCIATED(qs_ot_env%matrix_sinp_b)) CALL dbcsr_release_p(qs_ot_env%matrix_sinp_b)
      IF (ASSOCIATED(qs_ot_env%matrix_buf1)) CALL dbcsr_release_p(qs_ot_env%matrix_buf1)
      IF (ASSOCIATED(qs_ot_env%matrix_buf2)) CALL dbcsr_release_p(qs_ot_env%matrix_buf2)
      IF (ASSOCIATED(qs_ot_env%matrix_buf3)) CALL dbcsr_release_p(qs_ot_env%matrix_buf3)
      IF (ASSOCIATED(qs_ot_env%matrix_buf4)) CALL dbcsr_release_p(qs_ot_env%matrix_buf4)
      IF (ASSOCIATED(qs_ot_env%matrix_buf1_ortho)) CALL dbcsr_release_p(qs_ot_env%matrix_buf1_ortho)
      IF (ASSOCIATED(qs_ot_env%matrix_buf2_ortho)) CALL dbcsr_release_p(qs_ot_env%matrix_buf2_ortho)
      IF (ASSOCIATED(qs_ot_env%matrix_c0)) CALL dbcsr_release_p(qs_ot_env%matrix_c0)
      IF (ASSOCIATED(qs_ot_env%matrix_sc0)) CALL dbcsr_release_p(qs_ot_env%matrix_sc0)
      IF (ASSOCIATED(qs_ot_env%matrix_psc0)) CALL dbcsr_release_p(qs_ot_env%matrix_psc0)
      IF (ASSOCIATED(qs_ot_env%matrix_x)) CALL dbcsr_release_p(qs_ot_env%matrix_x)
      IF (ASSOCIATED(qs_ot_env%matrix_sx)) CALL dbcsr_release_p(qs_ot_env%matrix_sx)
      IF (ASSOCIATED(qs_ot_env%matrix_gx)) CALL dbcsr_release_p(qs_ot_env%matrix_gx)
      IF (ASSOCIATED(qs_ot_env%matrix_dx)) CALL dbcsr_release_p(qs_ot_env%matrix_dx)
      IF (ASSOCIATED(qs_ot_env%matrix_gx_old)) CALL dbcsr_release_p(qs_ot_env%matrix_gx_old)
      IF (ASSOCIATED(qs_ot_env%buf1_k_k_nosym)) CALL dbcsr_release_p(qs_ot_env%buf1_k_k_nosym)
      IF (ASSOCIATED(qs_ot_env%buf2_k_k_nosym)) CALL dbcsr_release_p(qs_ot_env%buf2_k_k_nosym)
      IF (ASSOCIATED(qs_ot_env%buf3_k_k_nosym)) CALL dbcsr_release_p(qs_ot_env%buf3_k_k_nosym)
      IF (ASSOCIATED(qs_ot_env%buf4_k_k_nosym)) CALL dbcsr_release_p(qs_ot_env%buf4_k_k_nosym)
      IF (ASSOCIATED(qs_ot_env%p_k_k_sym)) CALL dbcsr_release_p(qs_ot_env%p_k_k_sym)
      IF (ASSOCIATED(qs_ot_env%buf1_k_k_sym)) CALL dbcsr_release_p(qs_ot_env%buf1_k_k_sym)
      IF (ASSOCIATED(qs_ot_env%buf2_k_k_sym)) CALL dbcsr_release_p(qs_ot_env%buf2_k_k_sym)
      IF (ASSOCIATED(qs_ot_env%buf3_k_k_sym)) CALL dbcsr_release_p(qs_ot_env%buf3_k_k_sym)
      IF (ASSOCIATED(qs_ot_env%buf4_k_k_sym)) CALL dbcsr_release_p(qs_ot_env%buf4_k_k_sym)
      IF (ASSOCIATED(qs_ot_env%buf1_n_k)) CALL dbcsr_release_p(qs_ot_env%buf1_n_k)
      IF (ASSOCIATED(qs_ot_env%buf1_n_k_dp)) CALL dbcsr_release_p(qs_ot_env%buf1_n_k_dp)

      IF (qs_ot_env%settings%ot_method .EQ. "DIIS" .OR. &
          qs_ot_env%settings%ot_method .EQ. "BROY") THEN
         CALL dbcsr_deallocate_matrix_set(qs_ot_env%matrix_h_x)
         CALL dbcsr_deallocate_matrix_set(qs_ot_env%matrix_h_e)
         DEALLOCATE (qs_ot_env%ls_diis)
         DEALLOCATE (qs_ot_env%lss_diis)
         DEALLOCATE (qs_ot_env%c_diis)
         DEALLOCATE (qs_ot_env%c_broy)
         DEALLOCATE (qs_ot_env%energy_h)
         DEALLOCATE (qs_ot_env%ipivot)
      ENDIF

      IF (qs_ot_env%settings%do_rotation) THEN

         IF (ASSOCIATED(qs_ot_env%rot_mat_u)) CALL dbcsr_release_p(qs_ot_env%rot_mat_u)
         IF (ASSOCIATED(qs_ot_env%rot_mat_x)) CALL dbcsr_release_p(qs_ot_env%rot_mat_x)
         IF (ASSOCIATED(qs_ot_env%rot_mat_dedu)) CALL dbcsr_release_p(qs_ot_env%rot_mat_dedu)
         IF (ASSOCIATED(qs_ot_env%rot_mat_chc)) CALL dbcsr_release_p(qs_ot_env%rot_mat_chc)

         IF (qs_ot_env%settings%ot_method .EQ. "DIIS") THEN
            CALL dbcsr_deallocate_matrix_set(qs_ot_env%rot_mat_h_x)
            CALL dbcsr_deallocate_matrix_set(qs_ot_env%rot_mat_h_e)
         ENDIF

         DEALLOCATE (qs_ot_env%rot_mat_evals)

         IF (ASSOCIATED(qs_ot_env%rot_mat_evec)) CALL dbcsr_release_p(qs_ot_env%rot_mat_evec)
         IF (ASSOCIATED(qs_ot_env%rot_mat_gx)) CALL dbcsr_release_p(qs_ot_env%rot_mat_gx)
         IF (ASSOCIATED(qs_ot_env%rot_mat_gx_old)) CALL dbcsr_release_p(qs_ot_env%rot_mat_gx_old)
         IF (ASSOCIATED(qs_ot_env%rot_mat_dx)) CALL dbcsr_release_p(qs_ot_env%rot_mat_dx)
      ENDIF

      IF (qs_ot_env%settings%do_ener) THEN
         DEALLOCATE (qs_ot_env%ener_x)
         DEALLOCATE (qs_ot_env%ener_gx)
         IF (qs_ot_env%settings%ot_method .EQ. "DIIS") THEN
            DEALLOCATE (qs_ot_env%ener_h_x)
            DEALLOCATE (qs_ot_env%ener_h_e)
         ENDIF
         IF (qs_ot_env%use_dx) THEN
            DEALLOCATE (qs_ot_env%ener_dx)
         ENDIF
         IF (qs_ot_env%use_gx_old) THEN
            DEALLOCATE (qs_ot_env%ener_gx_old)
         ENDIF
      END IF

   END SUBROUTINE qs_ot_destroy

! **************************************************************************************************
!> \brief ...
!> \param settings ...
!> \param ot_section ...
!> \param output_unit ...
! **************************************************************************************************
   SUBROUTINE ot_readwrite_input(settings, ot_section, output_unit)
      TYPE(qs_ot_settings_type)                          :: settings
      TYPE(section_vals_type), POINTER                   :: ot_section
      INTEGER, INTENT(IN)                                :: output_unit

      CHARACTER(len=*), PARAMETER :: routineN = 'ot_readwrite_input', &
         routineP = moduleN//':'//routineN

      INTEGER                                            :: handle, ls_method, ot_algorithm, &
                                                            ot_method, ot_ortho_irac

      CALL timeset(routineN, handle)

      ! choose algorithm
      CALL section_vals_val_get(ot_section, "ALGORITHM", i_val=ot_algorithm)
      SELECT CASE (ot_algorithm)
      CASE (ot_algo_taylor_or_diag)
         settings%ot_algorithm = "TOD"
      CASE (ot_algo_irac)
         CALL cite_reference(Weber2008)
         settings%ot_algorithm = "REF"
      CASE DEFAULT
         CPABORT("Value unknown")
      END SELECT

      ! irac input
      CALL section_vals_val_get(ot_section, "IRAC_DEGREE", i_val=settings%irac_degree)
      IF (settings%irac_degree < 2 .OR. settings%irac_degree > 4) THEN
         CPABORT("READ OT IRAC_DEGREE: Value unknown")
      ENDIF
      CALL section_vals_val_get(ot_section, "MAX_IRAC", i_val=settings%max_irac)
      IF (settings%max_irac < 1) THEN
         CPABORT("READ OT MAX_IRAC: VALUE MUST BE GREATER THAN ZERO")
      ENDIF
      CALL section_vals_val_get(ot_section, "EPS_IRAC_FILTER_MATRIX", r_val=settings%eps_irac_filter_matrix)
      CALL section_vals_val_get(ot_section, "EPS_IRAC", r_val=settings%eps_irac)
      IF (settings%eps_irac < 0.0_dp) THEN
         CPABORT("READ OT EPS_IRAC: VALUE MUST BE GREATER THAN ZERO")
      ENDIF
      CALL section_vals_val_get(ot_section, "EPS_IRAC_QUICK_EXIT", r_val=settings%eps_irac_quick_exit)
      IF (settings%eps_irac_quick_exit < 0.0_dp) THEN
         CPABORT("READ OT EPS_IRAC_QUICK_EXIT: VALUE MUST BE GREATER THAN ZERO")
      ENDIF

      CALL section_vals_val_get(ot_section, "EPS_IRAC_SWITCH", r_val=settings%eps_irac_switch)
      IF (settings%eps_irac_switch < 0.0_dp) THEN
         CPABORT("READ OT EPS_IRAC_SWITCH: VALUE MUST BE GREATER THAN ZERO")
      ENDIF

      CALL section_vals_val_get(ot_section, "ORTHO_IRAC", i_val=ot_ortho_irac)
      SELECT CASE (ot_ortho_irac)
      CASE (ot_chol_irac)
         settings%ortho_irac = "CHOL"
      CASE (ot_poly_irac)
         settings%ortho_irac = "POLY"
      CASE (ot_lwdn_irac)
         settings%ortho_irac = "LWDN"
      CASE DEFAULT
         CPABORT("READ OT ORTHO_IRAC: Value unknown")
      END SELECT

      CALL section_vals_val_get(ot_section, "ON_THE_FLY_LOC", l_val=settings%on_the_fly_loc)

      CALL section_vals_val_get(ot_section, "MINIMIZER", i_val=ot_method)
      ! compatibility
      SELECT CASE (ot_method)
      CASE (ot_mini_sd)
         settings%ot_method = "SD"
      CASE (ot_mini_cg)
         settings%ot_method = "CG"
      CASE (ot_mini_diis)
         settings%ot_method = "DIIS"
         CALL section_vals_val_get(ot_section, "N_HISTORY_VEC", i_val=settings%diis_m)
      CASE (ot_mini_broyden)
         CALL section_vals_val_get(ot_section, "N_HISTORY_VEC", i_val=settings%diis_m)
         CALL section_vals_val_get(ot_section, "BROYDEN_BETA", r_val=settings%broyden_beta)
         CALL section_vals_val_get(ot_section, "BROYDEN_GAMMA", r_val=settings%broyden_gamma)
         CALL section_vals_val_get(ot_section, "BROYDEN_SIGMA", r_val=settings%broyden_sigma)
         CALL section_vals_val_get(ot_section, "BROYDEN_ETA", r_val=settings%broyden_eta)
         CALL section_vals_val_get(ot_section, "BROYDEN_OMEGA", r_val=settings%broyden_omega)
         CALL section_vals_val_get(ot_section, "BROYDEN_SIGMA_DECREASE", r_val=settings%broyden_sigma_decrease)
         CALL section_vals_val_get(ot_section, "BROYDEN_SIGMA_MIN", r_val=settings%broyden_sigma_min)
         CALL section_vals_val_get(ot_section, "BROYDEN_FORGET_HISTORY", l_val=settings%broyden_forget_history)
         CALL section_vals_val_get(ot_section, "BROYDEN_ADAPTIVE_SIGMA", l_val=settings%broyden_adaptive_sigma)
         CALL section_vals_val_get(ot_section, "BROYDEN_ENABLE_FLIP", l_val=settings%broyden_enable_flip)
         settings%ot_method = "BROY"
      CASE DEFAULT
         CPABORT("READ OTSCF MINIMIZER: Value unknown")
      END SELECT
      CALL section_vals_val_get(ot_section, "SAFER_DIIS", l_val=settings%safer_diis)
      CALL section_vals_val_get(ot_section, "LINESEARCH", i_val=ls_method)
      SELECT CASE (ls_method)
      CASE (ls_none)
         settings%line_search_method = "NONE"
      CASE (ls_2pnt)
         settings%line_search_method = "2PNT"
      CASE (ls_3pnt)
         settings%line_search_method = "3PNT"
      CASE (ls_gold)
         settings%line_search_method = "GOLD"
         CALL section_vals_val_get(ot_section, "GOLD_TARGET", r_val=settings%gold_target)
      CASE DEFAULT
         CPABORT("READ OTSCF LS: Value unknown")
      END SELECT

      CALL section_vals_val_get(ot_section, "PRECOND_SOLVER", i_val=settings%precond_solver_type)
      SELECT CASE (settings%precond_solver_type)
      CASE (ot_precond_solver_default)
         settings%precond_solver_name = "DEFAULT"
      CASE (ot_precond_solver_inv_chol)
         settings%precond_solver_name = "INVERSE_CHOLESKY"
      CASE (ot_precond_solver_direct)
         settings%precond_solver_name = "DIRECT"
      CASE (ot_precond_solver_update)
         settings%precond_solver_name = "INVERSE_UPDATE"
      CASE DEFAULT
         CPABORT("READ OTSCF SOLVER: Value unknown")
      END SELECT

      !If these values are negative we will set them "optimal" for a given precondtioner below
      CALL section_vals_val_get(ot_section, "STEPSIZE", r_val=settings%ds_min)
      CALL section_vals_val_get(ot_section, "ENERGY_GAP", r_val=settings%energy_gap)

      CALL section_vals_val_get(ot_section, "PRECONDITIONER", i_val=settings%preconditioner_type)
      SELECT CASE (settings%preconditioner_type)
      CASE (ot_precond_none)
         settings%preconditioner_name = "NONE"
         IF (settings%ds_min < 0.0_dp) settings%ds_min = 0.15_dp
         IF (settings%energy_gap < 0.0_dp) settings%energy_gap = 0.2_dp
      CASE (ot_precond_full_single)
         settings%preconditioner_name = "FULL_SINGLE"
         IF (settings%ds_min < 0.0_dp) settings%ds_min = 0.15_dp
         IF (settings%energy_gap < 0.0_dp) settings%energy_gap = 0.2_dp
      CASE (ot_precond_full_single_inverse)
         settings%preconditioner_name = "FULL_SINGLE_INVERSE"
         IF (settings%ds_min < 0.0_dp) settings%ds_min = 0.08_dp
         IF (settings%energy_gap < 0.0_dp) settings%energy_gap = 0.08_dp
      CASE (ot_precond_full_all)
         settings%preconditioner_name = "FULL_ALL"
         IF (settings%ds_min < 0.0_dp) settings%ds_min = 0.15_dp
         IF (settings%energy_gap < 0.0_dp) settings%energy_gap = 0.08_dp
      CASE (ot_precond_full_kinetic)
         settings%preconditioner_name = "FULL_KINETIC"
         IF (settings%ds_min < 0.0_dp) settings%ds_min = 0.15_dp
         IF (settings%energy_gap < 0.0_dp) settings%energy_gap = 0.2_dp
      CASE (ot_precond_s_inverse)
         settings%preconditioner_name = "FULL_S_INVERSE"
         IF (settings%ds_min < 0.0_dp) settings%ds_min = 0.15_dp
         IF (settings%energy_gap < 0.0_dp) settings%energy_gap = 0.2_dp
      CASE DEFAULT
         CPABORT("READ OTSCF PRECONDITIONER: Value unknown")
      END SELECT
      CALL section_vals_val_get(ot_section, "CHOLESKY", i_val=settings%cholesky_type)
      CALL section_vals_val_get(ot_section, "EPS_TAYLOR", r_val=settings%eps_taylor)
      CALL section_vals_val_get(ot_section, "MAX_TAYLOR", i_val=settings%max_taylor)
      CALL section_vals_val_get(ot_section, "ROTATION", l_val=settings%do_rotation)
      CALL section_vals_val_get(ot_section, "ENERGIES", l_val=settings%do_ener)
      CALL section_vals_val_get(ot_section, "OCCUPATION_PRECONDITIONER", &
                                l_val=settings%occupation_preconditioner)
      CALL section_vals_val_get(ot_section, "NONDIAG_ENERGY", l_val=settings%add_nondiag_energy)
      CALL section_vals_val_get(ot_section, "NONDIAG_ENERGY_STRENGTH", &
                                r_val=settings%nondiag_energy_strength)
      ! not yet fully implemented
      CPASSERT(.NOT. settings%do_ener)

      ! write OT output

      IF (output_unit > 0) THEN
         WRITE (output_unit, '(/,A)') "  ----------------------------------- OT ---------------------------------------"
         IF (settings%do_rotation) THEN
            WRITE (output_unit, '(A)') "  Allowing for rotations "
         END IF
         IF (settings%do_ener) THEN
            WRITE (output_unit, '(A,L2)') "  Optimizing orbital energies "
         END IF
         SELECT CASE (settings%OT_METHOD)
         CASE ("SD")
            WRITE (output_unit, '(A)') "  Minimizer      : SD                  : steepest descent"
         CASE ("CG")
            WRITE (output_unit, '(A)') "  Minimizer      : CG                  : conjugate gradient"
         CASE ("DIIS")
            WRITE (output_unit, '(A)') "  Minimizer      : DIIS                : direct inversion"
            WRITE (output_unit, '(A)') "                                         in the iterative subspace"
            WRITE (output_unit, '(A,I3,A)') "                                         using ", settings%diis_m, " DIIS vectors"
            IF (settings%safer_diis) THEN
               WRITE (output_unit, '(A,I3,A)') "                                         safer DIIS on"
            ELSE
               WRITE (output_unit, '(A,I3,A)') "                                         safer DIIS off"
            ENDIF
         CASE ("BROY")
            WRITE (output_unit, '(A)') "  Minimizer      : BROYDEN             : Broyden "
            WRITE (output_unit, '(A,F16.8)') "                   BETA                : ", settings%broyden_beta
            WRITE (output_unit, '(A,F16.8)') "                   GAMMA               : ", settings%broyden_gamma
            WRITE (output_unit, '(A,F16.8)') "                   SIGMA               : ", settings%broyden_sigma
            WRITE (output_unit, '(A,I3,A)') "                            using      : - ", &
               settings%diis_m, " BROYDEN vectors"
         CASE DEFAULT
            WRITE (output_unit, '(3A)') "  Minimizer      :      ", settings%OT_METHOD, " : UNKNOWN"
         END SELECT
         SELECT CASE (settings%preconditioner_name)
         CASE ("FULL_SINGLE")
            WRITE (output_unit, '(A)') "  Preconditioner : FULL_SINGLE         : diagonalization based"
         CASE ("FULL_SINGLE_INVERSE")
            WRITE (output_unit, '(A,/,A)') "  Preconditioner : FULL_SINGLE_INVERSE : inversion of ", &
               "                                         H + eS - 2*(Sc)(c^T*H*c+const)(Sc)^T"
         CASE ("FULL_ALL")
            WRITE (output_unit, '(A)') "  Preconditioner : FULL_ALL            : diagonalization, state selective"
         CASE ("FULL_KINETIC")
            WRITE (output_unit, '(A)') "  Preconditioner : FULL_KINETIC        : inversion of T + eS"
         CASE ("FULL_S_INVERSE")
            WRITE (output_unit, '(A)') "  Preconditioner : FULL_S_INVERSE      : cholesky inversion of S"
         CASE ("SPARSE_DIAG")
            WRITE (output_unit, '(A)') &
               "  Preconditioner : SPARSE_DIAG    : diagonal atomic block diagonalization"
         CASE ("SPARSE_KINETIC")
            WRITE (output_unit, '(A)') "  Preconditioner : SPARSE_KINETIC      : sparse linear solver for T + eS"
         CASE ("NONE")
            WRITE (output_unit, '(A)') "  Preconditioner : NONE"
         CASE DEFAULT
            WRITE (output_unit, '(3A)') "  Preconditioner : ", settings%preconditioner_name, " : UNKNOWN"
         END SELECT

         WRITE (output_unit, '(A)') "  Precond_solver : "//TRIM(settings%precond_solver_name)

         IF (settings%OT_METHOD .EQ. "SD" .OR. settings%OT_METHOD .EQ. "CG") THEN
            SELECT CASE (settings%line_search_method)
            CASE ("2PNT")
               WRITE (output_unit, '(A)') "  Line search    : 2PNT                : 2 energies, one gradient"
            CASE ("3PNT")
               WRITE (output_unit, '(A)') "  Line search    : 3PNT                : 3 energies"
            CASE ("GOLD")
               WRITE (output_unit, '(A)') "  Line search    : GOLD                : bracketing and golden section search"
               WRITE (output_unit, '(A,F14.8)') "                   target rel accuracy : ", settings%gold_target
            CASE ("NONE")
               WRITE (output_unit, '(A)') "  Line search    : NONE"
            CASE DEFAULT
               WRITE (output_unit, '(3A)') "  Line search : ", settings%line_search_method, " : UNKNOWN"
            END SELECT
         ENDIF
         WRITE (output_unit, '(A,F14.8,T49,A,F14.8)') "  stepsize       :", settings%ds_min, &
            "  energy_gap     :", settings%energy_gap
         IF (settings%ot_algorithm .EQ. 'TOD') THEN
            WRITE (output_unit, '(A,E14.5,T49,A,I14)') "  eps_taylor     :", settings%eps_taylor, &
               "  max_taylor     :", settings%max_taylor
         ENDIF
         IF (settings%ot_algorithm .EQ. 'REF') THEN
            WRITE (output_unit, '(A,1X,A,T49,A,I14)') "  ortho_irac     :", settings%ortho_irac, &
               "  irac_degree        :", settings%irac_degree
            WRITE (output_unit, '(A,I14,T49,A,E14.5)') "  max_irac       :", settings%max_irac, &
               "  eps_irac           :", settings%eps_irac
            WRITE (output_unit, '(A,E14.5,T49,A,E14.5)') "  eps_irac_switch:", settings%eps_irac_switch, &
               "  eps_irac_quick_exit:", settings%eps_irac_quick_exit
            WRITE (output_unit, '(A,L2)') "  on_the_fly_loc     :", settings%on_the_fly_loc
         END IF
         WRITE (output_unit, '(A)') "  ----------------------------------- OT ---------------------------------------"
         WRITE (UNIT=output_unit, &
                FMT="(/,T3,A,T12,A,T31,A,T39,A,T59,A,T75,A,/,T3,A)") &
            "Step", "Update method", "Time", "Convergence", "Total energy", "Change", &
            REPEAT("-", 78)
      END IF

      CALL timestop(handle)

   END SUBROUTINE ot_readwrite_input
! **************************************************************************************************

END MODULE qs_ot_types
