accint_weights_forces.F

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!--------------------------------------------------------------------------------------------------!
!   CP2K: A general program to perform molecular dynamics simulations                              !
!   Copyright 2000-2026 CP2K developers group <https://cp2k.org>                                   !
!                                                                                                  !
!   SPDX-License-Identifier: GPL-2.0-or-later                                                      !
!--------------------------------------------------------------------------------------------------!
 
! **************************************************************************************************
!> \brief
!> \author JGH (01.2026)
! **************************************************************************************************
MODULE accint_weights_forces
   USE ao_util,                         ONLY: exp_radius_very_extended
   USE atomic_kind_types,               ONLY: atomic_kind_type,&
                                              get_atomic_kind
   USE cell_types,                      ONLY: cell_type,&
                                              pbc
   USE cp_control_types,                ONLY: dft_control_type
   USE cp_log_handling,                 ONLY: cp_logger_get_default_io_unit
   USE grid_api,                        ONLY: integrate_pgf_product
   USE input_constants,                 ONLY: sic_none,&
                                              xc_none
   USE input_section_types,             ONLY: section_vals_type,&
                                              section_vals_val_get
   USE kinds,                           ONLY: dp
   USE memory_utilities,                ONLY: reallocate
   USE particle_types,                  ONLY: particle_type
   USE pw_env_types,                    ONLY: pw_env_get,&
                                              pw_env_type
   USE pw_grids,                        ONLY: pw_grid_compare
   USE pw_methods,                      ONLY: pw_axpy,&
                                              pw_multiply_with,&
                                              pw_scale,&
                                              pw_transfer,&
                                              pw_zero
   USE pw_pool_types,                   ONLY: pw_pool_p_type,&
                                              pw_pool_type
   USE pw_types,                        ONLY: pw_c1d_gs_type,&
                                              pw_r3d_rs_type
   USE qs_environment_types,            ONLY: get_qs_env,&
                                              qs_environment_type
   USE qs_force_types,                  ONLY: qs_force_type
   USE qs_fxc,                          ONLY: qs_fxc_analytic
   USE qs_ks_types,                     ONLY: get_ks_env,&
                                              qs_ks_env_type
   USE qs_rho_types,                    ONLY: qs_rho_create,&
                                              qs_rho_get,&
                                              qs_rho_set,&
                                              qs_rho_type
   USE realspace_grid_types,            ONLY: realspace_grid_type,&
                                              transfer_pw2rs
   USE skala_gpw_functional,            ONLY: skala_gpw_exc_density,&
                                              xc_section_uses_native_skala_grid
   USE virial_types,                    ONLY: virial_type
   USE xc,                              ONLY: xc_exc_pw_create,&
                                              xc_vxc_pw_create
#include "./base/base_uses.f90"
 
   IMPLICIT NONE
 
   PRIVATE
 
   LOGICAL, PRIVATE, PARAMETER :: debug_this_module = .false.
 
   CHARACTER(len=*), PARAMETER, PRIVATE :: moduleN = 'accint_weights_forces'
 
   PUBLIC :: accint_weight_force
 
CONTAINS
 
! **************************************************************************************************
!> \brief ...
!> \param qs_env ...
!> \param rho ...
!> \param rho1 ...
!> \param order ...
!> \param xc_section ...
!> \param triplet ...
!> \param force_scale ...
! **************************************************************************************************
   SUBROUTINE accint_weight_force(qs_env, rho, rho1, order, xc_section, triplet, force_scale)
      TYPE(qs_environment_type), POINTER                 :: qs_env
      TYPE(qs_rho_type), POINTER                         :: rho, rho1
      INTEGER, INTENT(IN)                                :: order
      TYPE(section_vals_type), POINTER                   :: xc_section
      LOGICAL, INTENT(IN), OPTIONAL                      :: triplet
      REAL(kind=dp), INTENT(IN), OPTIONAL                :: force_scale
 
      CHARACTER(len=*), PARAMETER :: routinen = 'accint_weight_force'
 
      INTEGER                                            :: atom_a, handle, iatom, ikind, natom, &
                                                            natom_of_kind, nkind, output_unit
      INTEGER, DIMENSION(:), POINTER                     :: atom_list
      LOGICAL                                            :: lr_triplet, native_grid_diagnostics, &
                                                            native_skala_grid, uf_grid, use_virial
      REAL(kind=dp)                                      :: my_force_scale
      REAL(kind=dp), ALLOCATABLE, DIMENSION(:)           :: calpha, cvalue
      REAL(kind=dp), ALLOCATABLE, DIMENSION(:, :)        :: aforce
      REAL(kind=dp), DIMENSION(3, 3)                     :: avirial
      TYPE(atomic_kind_type), DIMENSION(:), POINTER      :: atomic_kind_set
      TYPE(dft_control_type), POINTER                    :: dft_control
      TYPE(pw_env_type), POINTER                         :: pw_env
      TYPE(pw_pool_type), POINTER                        :: auxbas_pw_pool, xc_pw_pool
      TYPE(pw_r3d_rs_type)                               :: e_force_rspace, e_rspace
      TYPE(qs_force_type), DIMENSION(:), POINTER         :: force
      TYPE(qs_ks_env_type), POINTER                      :: ks_env
      TYPE(virial_type), POINTER                         :: virial
 
      CALL timeset(routinen, handle)
 
      CALL get_qs_env(qs_env, dft_control=dft_control)
 
      IF (dft_control%qs_control%gapw_control%accurate_xcint) THEN
 
         CALL get_qs_env(qs_env=qs_env, force=force, virial=virial)
         use_virial = virial%pv_availability .AND. (.NOT. virial%pv_numer)
 
         CALL get_qs_env(qs_env, natom=natom, nkind=nkind)
         ALLOCATE (aforce(3, natom))
         ALLOCATE (calpha(nkind), cvalue(nkind))
         cvalue = 1.0_dp
         calpha(1:nkind) = dft_control%qs_control%gapw_control%aw(1:nkind)
 
         CALL get_qs_env(qs_env, ks_env=ks_env, pw_env=pw_env)
         CALL pw_env_get(pw_env, auxbas_pw_pool=auxbas_pw_pool, xc_pw_pool=xc_pw_pool)
         uf_grid = .NOT. pw_grid_compare(auxbas_pw_pool%pw_grid, xc_pw_pool%pw_grid)
         IF (uf_grid) THEN
            CALL xc_pw_pool%create_pw(e_rspace)
         ELSE
            CALL auxbas_pw_pool%create_pw(e_rspace)
         END IF
 
         lr_triplet = .false.
         IF (PRESENT(triplet)) lr_triplet = triplet
         my_force_scale = 1.0_dp
         IF (PRESENT(force_scale)) my_force_scale = force_scale
 
         CALL xc_density(ks_env, rho, rho1, order, xc_section, lr_triplet, e_rspace)
 
         IF (uf_grid) THEN
            CALL auxbas_pw_pool%create_pw(e_force_rspace)
            block
               TYPE(pw_c1d_gs_type) :: e_g_aux, e_g_xc
               CALL xc_pw_pool%create_pw(e_g_xc)
               CALL auxbas_pw_pool%create_pw(e_g_aux)
               CALL pw_transfer(e_rspace, e_g_xc)
               CALL pw_transfer(e_g_xc, e_g_aux)
               CALL pw_transfer(e_g_aux, e_force_rspace)
               CALL auxbas_pw_pool%give_back_pw(e_g_aux)
               CALL xc_pw_pool%give_back_pw(e_g_xc)
            END block
            CALL pw_scale(e_force_rspace, e_force_rspace%pw_grid%dvol)
            CALL gauss_grid_force(e_force_rspace, qs_env, calpha, cvalue, aforce, avirial)
            CALL auxbas_pw_pool%give_back_pw(e_force_rspace)
         ELSE
            CALL pw_scale(e_rspace, e_rspace%pw_grid%dvol)
            CALL gauss_grid_force(e_rspace, qs_env, calpha, cvalue, aforce, avirial)
         END IF
 
         IF (uf_grid) THEN
            CALL xc_pw_pool%give_back_pw(e_rspace)
         ELSE
            CALL auxbas_pw_pool%give_back_pw(e_rspace)
         END IF
 
         CALL get_qs_env(qs_env, atomic_kind_set=atomic_kind_set)
         native_skala_grid = xc_section_uses_native_skala_grid(xc_section)
         native_grid_diagnostics = .false.
         IF (native_skala_grid) THEN
            CALL section_vals_val_get(xc_section, "XC_FUNCTIONAL%GAUXC%NATIVE_GRID_DIAGNOSTICS", &
                                      l_val=native_grid_diagnostics)
         END IF
         DO ikind = 1, nkind
            CALL get_atomic_kind(atomic_kind_set(ikind), natom=natom_of_kind, atom_list=atom_list)
            DO iatom = 1, natom_of_kind
               atom_a = atom_list(iatom)
               IF (native_grid_diagnostics) THEN
                  output_unit = cp_logger_get_default_io_unit()
                  IF (output_unit > 0) THEN
                     WRITE (unit=output_unit, fmt="(T2,A,1X,I0,3(1X,ES20.12))") &
                        "SKALA_GPW| Accurate-XCINT atom force", atom_a, my_force_scale*aforce(:, atom_a)
                  END IF
               END IF
               force(ikind)%rho_elec(1:3, iatom) = &
                  force(ikind)%rho_elec(1:3, iatom) + my_force_scale*aforce(1:3, atom_a)
            END DO
         END DO
         IF (use_virial) THEN
            virial%pv_exc = virial%pv_exc + my_force_scale*avirial
            virial%pv_virial = virial%pv_virial + my_force_scale*avirial
         END IF
 
         DEALLOCATE (aforce, calpha, cvalue)
 
      END IF
 
      CALL timestop(handle)
 
   END SUBROUTINE accint_weight_force
 
! **************************************************************************************************
!> \brief computes the forces/virial due to atomic centered Gaussian functions
!> \param e_rspace Energy density
!> \param qs_env ...
!> \param calpha ...
!> \param cvalue ...
!> \param aforce ...
!> \param avirial ...
! **************************************************************************************************
   SUBROUTINE gauss_grid_force(e_rspace, qs_env, calpha, cvalue, aforce, avirial)
      TYPE(pw_r3d_rs_type), INTENT(IN)                   :: e_rspace
      TYPE(qs_environment_type), POINTER                 :: qs_env
      REAL(kind=dp), DIMENSION(:), INTENT(IN)            :: calpha, cvalue
      REAL(kind=dp), DIMENSION(:, :), INTENT(OUT)        :: aforce
      REAL(kind=dp), DIMENSION(3, 3), INTENT(OUT)        :: avirial
 
      CHARACTER(len=*), PARAMETER                        :: routinen = 'gauss_grid_force'
 
      INTEGER                                            :: atom_a, handle, iatom, igrid, ikind, j, &
                                                            natom_of_kind, npme
      INTEGER, DIMENSION(:), POINTER                     :: atom_list, cores
      LOGICAL                                            :: use_virial
      REAL(kind=dp)                                      :: alpha, eps_rho_rspace, radius
      REAL(kind=dp), DIMENSION(3)                        :: force_a, force_b, ra
      REAL(kind=dp), DIMENSION(3, 3)                     :: my_virial_a, my_virial_b
      REAL(kind=dp), DIMENSION(:, :), POINTER            :: hab, pab
      TYPE(atomic_kind_type), DIMENSION(:), POINTER      :: atomic_kind_set
      TYPE(cell_type), POINTER                           :: cell
      TYPE(dft_control_type), POINTER                    :: dft_control
      TYPE(particle_type), DIMENSION(:), POINTER         :: particle_set
      TYPE(pw_env_type), POINTER                         :: pw_env
      TYPE(pw_pool_p_type), DIMENSION(:), POINTER        :: pw_pools
      TYPE(realspace_grid_type), DIMENSION(:), POINTER   :: rs_grids
      TYPE(realspace_grid_type), POINTER                 :: rs_v
 
      CALL timeset(routinen, handle)
 
      ALLOCATE (cores(1))
      ALLOCATE (hab(1, 1))
      ALLOCATE (pab(1, 1))
 
      NULLIFY (pw_pools, rs_grids, rs_v)
 
      CALL get_qs_env(qs_env, pw_env=pw_env)
      CALL pw_env_get(pw_env, pw_pools=pw_pools, rs_grids=rs_grids)
      DO igrid = 1, SIZE(pw_pools)
         IF (pw_grid_compare(e_rspace%pw_grid, pw_pools(igrid)%pool%pw_grid)) THEN
            rs_v => rs_grids(igrid)
            EXIT
         END IF
      END DO
      IF (.NOT. ASSOCIATED(rs_v)) THEN
         cpabort("No realspace grid for Accurate-XCINT weight force")
      END IF
 
      CALL transfer_pw2rs(rs_v, e_rspace)
 
      CALL get_qs_env(qs_env, &
                      atomic_kind_set=atomic_kind_set, &
                      cell=cell, &
                      dft_control=dft_control, &
                      particle_set=particle_set)
 
      use_virial = .true.
      avirial = 0.0_dp
      aforce = 0.0_dp
 
      eps_rho_rspace = dft_control%qs_control%eps_rho_rspace
 
      DO ikind = 1, SIZE(atomic_kind_set)
 
         CALL get_atomic_kind(atomic_kind_set(ikind), natom=natom_of_kind, atom_list=atom_list)
 
         alpha = calpha(ikind)
         pab(1, 1) = -cvalue(ikind)
         IF (alpha == 0.0_dp .OR. pab(1, 1) == 0.0_dp) cycle
 
         CALL reallocate(cores, 1, natom_of_kind)
         npme = 0
         cores = 0
 
         DO iatom = 1, natom_of_kind
            atom_a = atom_list(iatom)
            ra(:) = pbc(particle_set(atom_a)%r, cell)
            IF (rs_v%desc%parallel .AND. .NOT. rs_v%desc%distributed) THEN
               ! replicated realspace grid, split the atoms up between procs
               IF (modulo(iatom, rs_v%desc%group_size) == rs_v%desc%my_pos) THEN
                  npme = npme + 1
                  cores(npme) = iatom
               END IF
            ELSE
               npme = npme + 1
               cores(npme) = iatom
            END IF
         END DO
 
         DO j = 1, npme
 
            iatom = cores(j)
            atom_a = atom_list(iatom)
            ra(:) = pbc(particle_set(atom_a)%r, cell)
            hab(1, 1) = 0.0_dp
            force_a(:) = 0.0_dp
            force_b(:) = 0.0_dp
            my_virial_a = 0.0_dp
            my_virial_b = 0.0_dp
 
            radius = exp_radius_very_extended(la_min=0, la_max=0, lb_min=0, lb_max=0, &
                                              ra=ra, rb=ra, rp=ra, &
                                              zetp=alpha, eps=eps_rho_rspace, &
                                              pab=pab, o1=0, o2=0, &
                                              prefactor=1.0_dp, cutoff=1.0_dp)
 
            CALL integrate_pgf_product(0, alpha, 0, &
                                       0, 0.0_dp, 0, ra, [0.0_dp, 0.0_dp, 0.0_dp], &
                                       rs_v, hab, pab=pab, o1=0, o2=0, &
                                       radius=radius, &
                                       calculate_forces=.true., force_a=force_a, &
                                       force_b=force_b, use_virial=use_virial, my_virial_a=my_virial_a, &
                                       my_virial_b=my_virial_b, use_subpatch=.true., subpatch_pattern=0)
 
            aforce(1:3, atom_a) = aforce(1:3, atom_a) + force_a(1:3)
            avirial = avirial + my_virial_a
 
         END DO
 
      END DO
 
      DEALLOCATE (hab, pab, cores)
 
      CALL timestop(handle)
 
   END SUBROUTINE gauss_grid_force
 
! **************************************************************************************************
!> \brief calculates the XC density:
!>        order=0: exc will contain the xc energy density E_xc(r)
!>        order=1: exc will contain V_xc(r) * rho1(r)
!>        order=2: exc will contain F_xc(r) * rho1(r) * rho1(r)
!> \param ks_env to get all the needed things
!> \param rho_struct density
!> \param rho1_struct response density
!> \param order requested derivative order
!> \param xc_section ...
!> \param triplet ...
!> \param exc ...
!> \author JGH
! **************************************************************************************************
   SUBROUTINE xc_density(ks_env, rho_struct, rho1_struct, order, xc_section, triplet, exc)
 
      TYPE(qs_ks_env_type), POINTER                      :: ks_env
      TYPE(qs_rho_type), POINTER                         :: rho_struct, rho1_struct
      INTEGER, INTENT(IN)                                :: order
      TYPE(section_vals_type), POINTER                   :: xc_section
      LOGICAL, INTENT(IN)                                :: triplet
      TYPE(pw_r3d_rs_type)                               :: exc
 
      CHARACTER(len=*), PARAMETER                        :: routinen = 'xc_density'
 
      INTEGER                                            :: handle, ispin, myfun, nspins
      LOGICAL :: native_skala_grid, rho1_g_valid, rho1_tau_g_valid, rho1_tau_valid, rho_g_valid, &
         rho_tau_g_valid, rho_tau_valid, uf_grid
      REAL(kind=dp)                                      :: excint, factor
      REAL(kind=dp), DIMENSION(3, 3)                     :: vdum
      TYPE(cell_type), POINTER                           :: cell
      TYPE(dft_control_type), POINTER                    :: dft_control
      TYPE(particle_type), DIMENSION(:), POINTER         :: particle_set
      TYPE(pw_c1d_gs_type), DIMENSION(:), POINTER        :: rho1_g, rho1_g_base, rho_g, rho_g_base, &
                                                            tau1_g, tau1_g_base, tau_g, tau_g_base
      TYPE(pw_c1d_gs_type), POINTER                      :: rho_nlcc_g, rho_nlcc_g_use, rho_nlcc_g_xc
      TYPE(pw_env_type), POINTER                         :: pw_env
      TYPE(pw_pool_type), POINTER                        :: auxbas_pw_pool, xc_pw_pool
      TYPE(pw_r3d_rs_type), DIMENSION(:), POINTER        :: rho1_r, rho1_r_base, rho_r, rho_r_base, &
                                                            tau1_r, tau1_r_base, tau_r, &
                                                            tau_r_base, vxc_rho, vxc_tau
      TYPE(pw_r3d_rs_type), POINTER                      :: rho_nlcc, rho_nlcc_use, rho_nlcc_xc, &
                                                            weights
      TYPE(qs_rho_type), POINTER                         :: rho_fxc
 
      CALL timeset(routinen, handle)
 
      ! we always get true exc (not integration weighted)
      NULLIFY (rho1_g, rho1_g_base, rho1_r, rho1_r_base, rho_fxc, tau1_g, tau1_g_base)
      NULLIFY (rho_g, rho_g_base, rho_r, rho_r_base, tau_g, tau_g_base, tau_r, tau_r_base, &
               tau1_r, tau1_r_base)
      NULLIFY (particle_set, rho_nlcc_use, rho_nlcc_xc, rho_nlcc_g_use, rho_nlcc_g_xc, weights)
 
      CALL get_ks_env(ks_env, &
                      dft_control=dft_control, &
                      pw_env=pw_env, &
                      cell=cell, &
                      particle_set=particle_set, &
                      rho_nlcc=rho_nlcc, &
                      rho_nlcc_g=rho_nlcc_g)
 
      CALL qs_rho_get(rho_struct, rho_r=rho_r_base, rho_g=rho_g_base, tau_r=tau_r_base, &
                      tau_g=tau_g_base, rho_g_valid=rho_g_valid, tau_g_valid=rho_tau_g_valid, &
                      tau_r_valid=rho_tau_valid)
      rho_r => rho_r_base
      rho_g => rho_g_base
      tau_r => tau_r_base
      tau_g => tau_g_base
 
      nspins = dft_control%nspins
 
      CALL section_vals_val_get(xc_section, "XC_FUNCTIONAL%_SECTION_PARAMETERS_", i_val=myfun)
      native_skala_grid = xc_section_uses_native_skala_grid(xc_section)
 
      CALL pw_env_get(pw_env, xc_pw_pool=xc_pw_pool, auxbas_pw_pool=auxbas_pw_pool)
      uf_grid = .NOT. pw_grid_compare(auxbas_pw_pool%pw_grid, xc_pw_pool%pw_grid)
      IF (uf_grid) THEN
         NULLIFY (rho_r, rho_g, tau_r, tau_g)
         IF (rho_g_valid) THEN
            CALL create_density_on_pool(xc_pw_pool, rho_g_base, rho_r, rho_g)
         ELSEIF (ASSOCIATED(rho_r_base)) THEN
            CALL create_density_on_pool_from_r(auxbas_pw_pool, xc_pw_pool, rho_r_base, rho_r, rho_g)
         ELSE
            cpabort("Fine Grid in xc_density requires rho_r or rho_g")
         END IF
         IF (rho_tau_valid) THEN
            IF (rho_tau_g_valid) THEN
               CALL create_density_on_pool(xc_pw_pool, tau_g_base, tau_r, tau_g)
            ELSEIF (ASSOCIATED(tau_r_base)) THEN
               CALL create_density_on_pool_from_r(auxbas_pw_pool, xc_pw_pool, tau_r_base, tau_r, tau_g)
            ELSE
               cpabort("Fine Grid in xc_density requires tau_r or tau_g")
            END IF
         END IF
         IF (ASSOCIATED(rho_nlcc)) THEN
            ALLOCATE (rho_nlcc_g_xc, rho_nlcc_xc)
            CALL xc_pw_pool%create_pw(rho_nlcc_g_xc)
            CALL xc_pw_pool%create_pw(rho_nlcc_xc)
            CALL pw_transfer(rho_nlcc_g, rho_nlcc_g_xc)
            CALL pw_transfer(rho_nlcc_g_xc, rho_nlcc_xc)
            rho_nlcc_use => rho_nlcc_xc
            rho_nlcc_g_use => rho_nlcc_g_xc
         END IF
      END IF
      IF (.NOT. ASSOCIATED(rho_nlcc_use)) THEN
         rho_nlcc_use => rho_nlcc
         rho_nlcc_g_use => rho_nlcc_g
      END IF
 
      CALL pw_zero(exc)
 
      IF (myfun /= xc_none) THEN
 
         cpassert(ASSOCIATED(rho_struct))
         cpassert(dft_control%sic_method_id == sic_none)
 
         ! add the nlcc densities
         IF (ASSOCIATED(rho_nlcc_use) .AND. order <= 1) THEN
            factor = 1.0_dp
            DO ispin = 1, nspins
               CALL pw_axpy(rho_nlcc_use, rho_r(ispin), factor)
               CALL pw_axpy(rho_nlcc_g_use, rho_g(ispin), factor)
            END DO
         END IF
 
         NULLIFY (vxc_rho, vxc_tau)
         SELECT CASE (order)
         CASE (0)
            IF (native_skala_grid) THEN
               CALL skala_gpw_exc_density(exc, rho_r, rho_g, tau_r, xc_section, weights, &
                                          xc_pw_pool, particle_set, cell)
            ELSE
               ! we could reduce to energy only here
               CALL xc_exc_pw_create(rho_r, rho_g, tau_r, xc_section, weights, xc_pw_pool, exc)
            END IF
         CASE (1)
            IF (native_skala_grid) THEN
               CALL cp_abort(__location__, &
                             "Native SKALA GAPW accurate-XCINT response forces are not implemented.")
            END IF
            CALL qs_rho_get(rho1_struct, rho_r=rho1_r_base, rho_g=rho1_g_base, tau_r=tau1_r_base, &
                            tau_g=tau1_g_base, rho_g_valid=rho1_g_valid, &
                            tau_g_valid=rho1_tau_g_valid, tau_r_valid=rho1_tau_valid)
            rho1_r => rho1_r_base
            tau1_g => tau1_g_base
            tau1_r => tau1_r_base
            IF (uf_grid) THEN
               NULLIFY (rho1_r, rho1_g, tau1_r, tau1_g)
               IF (rho1_g_valid) THEN
                  CALL create_density_on_pool(xc_pw_pool, rho1_g_base, rho1_r, rho1_g)
               ELSEIF (ASSOCIATED(rho1_r_base)) THEN
                  CALL create_density_on_pool_from_r(auxbas_pw_pool, xc_pw_pool, rho1_r_base, rho1_r, rho1_g)
               ELSE
                  cpabort("Fine Grid in xc_density requires rho1_r or rho1_g")
               END IF
               IF (rho1_tau_valid) THEN
                  IF (rho1_tau_g_valid) THEN
                     CALL create_density_on_pool(xc_pw_pool, tau1_g_base, tau1_r, tau1_g)
                  ELSEIF (ASSOCIATED(tau1_r_base)) THEN
                     CALL create_density_on_pool_from_r(auxbas_pw_pool, xc_pw_pool, tau1_r_base, tau1_r, tau1_g)
                  ELSE
                     cpabort("Fine Grid in xc_density requires tau1_r or tau1_g")
                  END IF
               END IF
            END IF
            CALL xc_vxc_pw_create(vxc_rho=vxc_rho, vxc_tau=vxc_tau, rho_r=rho_r, &
                                  rho_g=rho_g, tau=tau_r, exc=excint, &
                                  xc_section=xc_section, &
                                  weights=weights, pw_pool=xc_pw_pool, &
                                  compute_virial=.false., &
                                  virial_xc=vdum)
         CASE (2)
            IF (native_skala_grid) THEN
               CALL cp_abort(__location__, &
                             "Native SKALA GAPW accurate-XCINT response forces are not implemented.")
            END IF
            CALL qs_rho_get(rho1_struct, rho_r=rho1_r_base, rho_g=rho1_g_base, tau_r=tau1_r_base, &
                            tau_g=tau1_g_base, rho_g_valid=rho1_g_valid, &
                            tau_g_valid=rho1_tau_g_valid, tau_r_valid=rho1_tau_valid)
            rho1_r => rho1_r_base
            tau1_g => tau1_g_base
            tau1_r => tau1_r_base
            IF (uf_grid) THEN
               NULLIFY (rho1_r, rho1_g, tau1_r, tau1_g)
               IF (rho1_g_valid) THEN
                  CALL create_density_on_pool(xc_pw_pool, rho1_g_base, rho1_r, rho1_g)
               ELSEIF (ASSOCIATED(rho1_r_base)) THEN
                  CALL create_density_on_pool_from_r(auxbas_pw_pool, xc_pw_pool, rho1_r_base, rho1_r, rho1_g)
               ELSE
                  cpabort("Fine Grid in xc_density requires rho1_r or rho1_g")
               END IF
               IF (rho1_tau_valid) THEN
                  IF (rho1_tau_g_valid) THEN
                     CALL create_density_on_pool(xc_pw_pool, tau1_g_base, tau1_r, tau1_g)
                  ELSEIF (ASSOCIATED(tau1_r_base)) THEN
                     CALL create_density_on_pool_from_r(auxbas_pw_pool, xc_pw_pool, tau1_r_base, tau1_r, tau1_g)
                  ELSE
                     cpabort("Fine Grid in xc_density requires tau1_r or tau1_g")
                  END IF
               END IF
               ALLOCATE (rho_fxc)
               CALL qs_rho_create(rho_fxc)
               IF (rho_tau_valid) THEN
                  CALL qs_rho_set(rho_fxc, rho_r=rho_r, rho_g=rho_g, tau_r=tau_r, &
                                  rho_r_valid=.true., rho_g_valid=.true., tau_r_valid=.true.)
               ELSE
                  CALL qs_rho_set(rho_fxc, rho_r=rho_r, rho_g=rho_g, &
                                  rho_r_valid=.true., rho_g_valid=.true.)
               END IF
            ELSE
               rho_fxc => rho_struct
            END IF
            CALL qs_fxc_analytic(rho_fxc, rho1_r, tau1_r, xc_section, weights, xc_pw_pool, &
                                 triplet, vxc_rho, vxc_tau)
            IF (uf_grid) DEALLOCATE (rho_fxc)
         CASE DEFAULT
            cpabort("Derivative order not available in xc_density")
         END SELECT
 
         ! remove the nlcc densities (keep stuff in original state)
         IF (ASSOCIATED(rho_nlcc_use) .AND. order <= 1) THEN
            factor = -1.0_dp
            DO ispin = 1, dft_control%nspins
               CALL pw_axpy(rho_nlcc_use, rho_r(ispin), factor)
               CALL pw_axpy(rho_nlcc_g_use, rho_g(ispin), factor)
            END DO
         END IF
         !
         SELECT CASE (order)
         CASE (0)
            !
         CASE (1, 2)
            CALL pw_zero(exc)
            IF (ASSOCIATED(vxc_rho)) THEN
               DO ispin = 1, nspins
                  CALL pw_multiply_with(vxc_rho(ispin), rho1_r(ispin))
                  CALL pw_axpy(vxc_rho(ispin), exc, 1.0_dp)
                  CALL vxc_rho(ispin)%release()
               END DO
               DEALLOCATE (vxc_rho)
            END IF
            IF (ASSOCIATED(vxc_tau)) THEN
               IF (.NOT. ASSOCIATED(tau1_r)) &
                  cpabort("Tau response density required for mGGA xc_density")
               DO ispin = 1, nspins
                  CALL pw_multiply_with(vxc_tau(ispin), tau1_r(ispin))
                  CALL pw_axpy(vxc_tau(ispin), exc, 1.0_dp)
                  CALL vxc_tau(ispin)%release()
               END DO
               DEALLOCATE (vxc_tau)
            END IF
         CASE DEFAULT
            cpabort("Derivative order not available in xc_density")
         END SELECT
 
         IF (order == 2) THEN
            CALL pw_scale(exc, 0.5_dp)
         END IF
 
      END IF
 
      IF (uf_grid) THEN
         CALL give_back_density_on_pool(xc_pw_pool, rho_r, rho_g)
         IF (ASSOCIATED(tau_r)) CALL give_back_density_on_pool(xc_pw_pool, tau_r, tau_g)
         IF (ASSOCIATED(rho1_r)) CALL give_back_density_on_pool(xc_pw_pool, rho1_r, rho1_g)
         IF (ASSOCIATED(tau1_r)) CALL give_back_density_on_pool(xc_pw_pool, tau1_r, tau1_g)
         IF (ASSOCIATED(rho_nlcc_xc)) THEN
            CALL xc_pw_pool%give_back_pw(rho_nlcc_xc)
            DEALLOCATE (rho_nlcc_xc)
         END IF
         IF (ASSOCIATED(rho_nlcc_g_xc)) THEN
            CALL xc_pw_pool%give_back_pw(rho_nlcc_g_xc)
            DEALLOCATE (rho_nlcc_g_xc)
         END IF
      END IF
 
      CALL timestop(handle)
 
   END SUBROUTINE xc_density
 
! **************************************************************************************************
!> \brief transfers a g-space density to a given PW pool and creates its r-space representation
!> \param pw_pool ...
!> \param rho_g_in ...
!> \param rho_r_out ...
!> \param rho_g_out ...
! **************************************************************************************************
   SUBROUTINE create_density_on_pool(pw_pool, rho_g_in, rho_r_out, rho_g_out)
      TYPE(pw_pool_type), POINTER                        :: pw_pool
      TYPE(pw_c1d_gs_type), DIMENSION(:), POINTER        :: rho_g_in
      TYPE(pw_r3d_rs_type), DIMENSION(:), POINTER        :: rho_r_out
      TYPE(pw_c1d_gs_type), DIMENSION(:), POINTER        :: rho_g_out
 
      INTEGER                                            :: ispin, nspins
 
      cpassert(ASSOCIATED(pw_pool))
      cpassert(ASSOCIATED(rho_g_in))
 
      nspins = SIZE(rho_g_in)
      ALLOCATE (rho_r_out(nspins), rho_g_out(nspins))
      DO ispin = 1, nspins
         CALL pw_pool%create_pw(rho_g_out(ispin))
         CALL pw_pool%create_pw(rho_r_out(ispin))
         CALL pw_transfer(rho_g_in(ispin), rho_g_out(ispin))
         CALL pw_transfer(rho_g_out(ispin), rho_r_out(ispin))
      END DO
 
   END SUBROUTINE create_density_on_pool
 
! **************************************************************************************************
!> \brief transfers an r-space density to a given PW pool and creates its g-space representation
!> \param source_pw_pool ...
!> \param target_pw_pool ...
!> \param rho_r_in ...
!> \param rho_r_out ...
!> \param rho_g_out ...
! **************************************************************************************************
   SUBROUTINE create_density_on_pool_from_r(source_pw_pool, target_pw_pool, rho_r_in, rho_r_out, rho_g_out)
      TYPE(pw_pool_type), POINTER                        :: source_pw_pool, target_pw_pool
      TYPE(pw_r3d_rs_type), DIMENSION(:), POINTER        :: rho_r_in, rho_r_out
      TYPE(pw_c1d_gs_type), DIMENSION(:), POINTER        :: rho_g_out
 
      INTEGER                                            :: ispin, nspins
      TYPE(pw_c1d_gs_type)                               :: rho_g_in
 
      cpassert(ASSOCIATED(source_pw_pool))
      cpassert(ASSOCIATED(target_pw_pool))
      cpassert(ASSOCIATED(rho_r_in))
 
      nspins = SIZE(rho_r_in)
      ALLOCATE (rho_r_out(nspins), rho_g_out(nspins))
      DO ispin = 1, nspins
         CALL source_pw_pool%create_pw(rho_g_in)
         CALL target_pw_pool%create_pw(rho_g_out(ispin))
         CALL target_pw_pool%create_pw(rho_r_out(ispin))
         CALL pw_transfer(rho_r_in(ispin), rho_g_in)
         CALL pw_transfer(rho_g_in, rho_g_out(ispin))
         CALL pw_transfer(rho_g_out(ispin), rho_r_out(ispin))
         CALL source_pw_pool%give_back_pw(rho_g_in)
      END DO
 
   END SUBROUTINE create_density_on_pool_from_r
 
! **************************************************************************************************
!> \brief returns temporary density arrays to the given PW pool
!> \param pw_pool ...
!> \param rho_r ...
!> \param rho_g ...
! **************************************************************************************************
   SUBROUTINE give_back_density_on_pool(pw_pool, rho_r, rho_g)
      TYPE(pw_pool_type), POINTER                        :: pw_pool
      TYPE(pw_r3d_rs_type), DIMENSION(:), POINTER        :: rho_r
      TYPE(pw_c1d_gs_type), DIMENSION(:), POINTER        :: rho_g
 
      INTEGER                                            :: ispin
 
      cpassert(ASSOCIATED(pw_pool))
 
      IF (ASSOCIATED(rho_r)) THEN
         DO ispin = 1, SIZE(rho_r)
            CALL pw_pool%give_back_pw(rho_r(ispin))
         END DO
         DEALLOCATE (rho_r)
      END IF
      IF (ASSOCIATED(rho_g)) THEN
         DO ispin = 1, SIZE(rho_g)
            CALL pw_pool%give_back_pw(rho_g(ispin))
         END DO
         DEALLOCATE (rho_g)
      END IF
 
   END SUBROUTINE give_back_density_on_pool
 
END MODULE accint_weights_forces