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xc_b97_fxc.F
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!--------------------------------------------------------------------------------------------------!
! CP2K: A general program to perform molecular dynamics simulations !
! Copyright 2000-2025 CP2K developers group <https://cp2k.org> !
! !
! SPDX-License-Identifier: GPL-2.0-or-later !
!--------------------------------------------------------------------------------------------------!
! **************************************************************************************************
!> \brief calculates fxc in the spirit of the b97 exchange/correlation functional
!> \author jgh
! **************************************************************************************************
MODULE xc_b97_fxc
USE kinds, ONLY: dp
USE pw_types, ONLY: pw_r3d_rs_type
#include "../base/base_uses.f90"
IMPLICIT NONE
PRIVATE
PUBLIC :: b97_fxc_eval, b97_fcc_eval
CONTAINS
! **************************************************************************************************
!> \brief ...
!> \param rhos ...
!> \param norm_drhos ...
!> \param fxc ...
!> \param gx ...
!> \param cx ...
!> \param eps_rho ...
! **************************************************************************************************
SUBROUTINE b97_fxc_eval(rhos, norm_drhos, fxc, gx, cx, eps_rho)
TYPE(pw_r3d_rs_type), INTENT(IN) :: rhos, norm_drhos
TYPE(pw_r3d_rs_type), INTENT(INOUT) :: fxc
REAL(KIND=dp), INTENT(IN) :: gx
REAL(KIND=dp), DIMENSION(:), INTENT(IN) :: cx
REAL(KIND=dp), INTENT(IN) :: eps_rho
CHARACTER(len=*), PARAMETER :: routineN = 'b97_fxc_eval'
INTEGER :: handle, i, io, j, k, norder
INTEGER, DIMENSION(2, 3) :: bo
REAL(KIND=dp) :: drho, gval, rho, sval, ux
CALL timeset(routineN, handle)
norder = SIZE(cx)
bo(1:2, 1:3) = rhos%pw_grid%bounds_local(1:2, 1:3)
!$OMP PARALLEL DO PRIVATE(i,j,k,io,rho,drho,sval,gval,ux) DEFAULT(NONE)&
!$OMP SHARED(bo,rhos,norm_drhos,fxc,gx,cx,eps_rho,norder)
DO k = bo(1, 3), bo(2, 3)
DO j = bo(1, 2), bo(2, 2)
DO i = bo(1, 1), bo(2, 1)
rho = rhos%array(i, j, k)
drho = norm_drhos%array(i, j, k)
IF (rho > eps_rho) THEN
sval = gx*(drho/rho**1.33333333333333_dp)**2
ux = sval/(1._dp + sval)
gval = 0.0_dp
DO io = 0, norder - 1
gval = gval + cx(io + 1)*(ux**io)
END DO
fxc%array(i, j, k) = fxc%array(i, j, k)*gval
END IF
END DO
END DO
END DO
CALL timestop(handle)
END SUBROUTINE b97_fxc_eval
! **************************************************************************************************
!> \brief ...
!> \param rhoa ...
!> \param rhob ...
!> \param norm_drhoa ...
!> \param norm_drhob ...
!> \param fcc ...
!> \param gcc ...
!> \param cco ...
!> \param eps_rho ...
! **************************************************************************************************
SUBROUTINE b97_fcc_eval(rhoa, rhob, norm_drhoa, norm_drhob, fcc, gcc, cco, eps_rho)
TYPE(pw_r3d_rs_type), INTENT(IN) :: rhoa, rhob, norm_drhoa, norm_drhob
TYPE(pw_r3d_rs_type), INTENT(INOUT) :: fcc
REAL(KIND=dp), INTENT(IN) :: gcc
REAL(KIND=dp), DIMENSION(:), INTENT(IN) :: cco
REAL(KIND=dp), INTENT(IN) :: eps_rho
CHARACTER(len=*), PARAMETER :: routineN = 'b97_fcc_eval'
INTEGER :: handle, i, io, j, k, norder
INTEGER, DIMENSION(2, 3) :: bo
REAL(KIND=dp) :: dra, drb, gval, ra, rb, sa, sb, sval, ux
CALL timeset(routineN, handle)
norder = SIZE(cco)
bo(1:2, 1:3) = rhoa%pw_grid%bounds_local(1:2, 1:3)
!$OMP PARALLEL DO PRIVATE(i,j,k,ra,rb,dra,drb,sa,sb,sval,gval,ux,io) DEFAULT(NONE)&
!$OMP SHARED(bo,rhoa,rhob,norm_drhoa,norm_drhob,fcc,gcc,cco,norder,eps_rho)
DO k = bo(1, 3), bo(2, 3)
DO j = bo(1, 2), bo(2, 2)
DO i = bo(1, 1), bo(2, 1)
ra = rhoa%array(i, j, k)
rb = rhob%array(i, j, k)
dra = norm_drhoa%array(i, j, k)
drb = norm_drhob%array(i, j, k)
IF (ra > eps_rho .AND. rb > eps_rho) THEN
sa = (dra/ra**1.33333333333333_dp)**2
sb = (drb/rb**1.33333333333333_dp)**2
sval = 0.5_dp*gcc*(sa + sb)
ux = sval/(1._dp + sval)
gval = 0.0_dp
DO io = 0, norder - 1
gval = gval + cco(io + 1)*(ux**io)
END DO
fcc%array(i, j, k) = fcc%array(i, j, k)*gval
END IF
END DO
END DO
END DO
CALL timestop(handle)
END SUBROUTINE b97_fcc_eval
END MODULE xc_b97_fxc