!
! Copyright (C) 2001 PWSCF group
! This file is distributed under the terms of the
! GNU General Public License. See the file `License'
! in the root directory of the present distribution,
! or http://www.gnu.org/copyleft/gpl.txt .
!
!-----------------------------------------------------------------------
subroutine setup_dgc
  !-----------------------------------------------------------------------
  ! Allocate and setup all variable needed in the gradient correction case
  !
  !  GGA+LSDA is allowed. AdC (September 1999).
  !  GGA+LSDA+NLCC is allowed. AdC (November 1999).
  !
#include "f_defs.h"

  use pwcom
  USE kinds, only : DP
  use phcom
  use funct, only : dft_is_gradient, gcxc, gcx_spin, gcc_spin
  implicit none
  integer :: k, is
  real(DP) :: grho2 (2), rh, zeta, grh2, fac, sx, sc, &
       v1x, v2x, v1c, v2c, vrrx, vsrx, vssx, vrrc, vsrc, vssc, v1xup, &
       v1xdw, v2xup, v2xdw, v1cup, v1cdw, vrrxup, vrrxdw, vrsxup, vrsxdw, &
       vssxup, vssxdw, vrrcup, vrrcdw, vrscup, vrscdw, vrzcup, vrzcdw
  real (DP), parameter :: epsr = 1.0d-6, epsg = 1.0d-10

  if ( .not. dft_is_gradient() ) return
  allocate (dvxc_rr(  nrxx , nspin , nspin))    
  allocate (dvxc_sr(  nrxx , nspin , nspin))    
  allocate (dvxc_ss(  nrxx , nspin , nspin))    
  allocate (dvxc_s (  nrxx , nspin , nspin))    
  allocate (grho   (  3    , nrxx  , nspin))    

  dvxc_rr(:,:,:) = 0.d0
  dvxc_sr(:,:,:) = 0.d0
  dvxc_ss(:,:,:) = 0.d0
  dvxc_s (:,:,:) = 0.d0
  grho   (:,:,:) = 0.d0
  !
  !    add rho_core
  !
  fac = 1.d0 / DBLE (nspin)
  if (nlcc_any) then
     do is = 1, nspin
        do k = 1, nrxx
           rho (k, is) = rho (k, is) + rho_core (k) * fac
        enddo
     enddo
  endif
  do is = 1, nspin
     call gradient (nrx1, nrx2, nrx3, nr1, nr2, nr3, nrxx, rho (1, is), &
          ngm, g, nl, alat, grho (1, 1, is) )
  enddo
  do k = 1, nrxx
     grho2 (1) = grho (1, k, 1) **2 + grho (2, k, 1) **2 + grho (3, k, 1) **2
     if (nspin == 1) then
        if (abs (rho (k, 1) ) > epsr .and. grho2 (1) > epsg) then
           call gcxc (rho (k, nspin), grho2(1), sx, sc, v1x, v2x, v1c, v2c)
           call dgcxc (rho (k, nspin), grho2, vrrx, vsrx, vssx, vrrc, &
                vsrc, vssc)
           dvxc_rr (k, 1, 1) = e2 * (vrrx + vrrc)
           dvxc_sr (k, 1, 1) = e2 * (vsrx + vsrc)
           dvxc_ss (k, 1, 1) = e2 * (vssx + vssc)
           dvxc_s (k, 1, 1) = e2 * (v2x + v2c)
        endif
     else
        grho2 (2) = grho (1, k, 2) **2 + grho (2, k, 2) **2 + grho (3, &
             k, 2) **2
        rh = rho (k, 1) + rho (k, 2)

        grh2 = (grho (1, k, 1) + grho (1, k, 2) ) **2 + (grho (2, k, 1) &
             + grho (2, k, 2) ) **2 + (grho (3, k, 1) + grho (3, k, 2) ) ** 2

        call gcx_spin (rho (k, 1), rho (k, 2), grho2 (1), grho2 (2), &
             sx, v1xup, v1xdw, v2xup, v2xdw)

        call dgcxc_spin (rho (k, 1), rho (k, 2), grho (1, k, 1), &
             grho (1, k, 2), vrrxup, vrrxdw, vrsxup, vrsxdw, vssxup, vssxdw, &
             vrrcup, vrrcdw, vrscup, vrscdw, vssc, vrzcup, vrzcdw)
        if (rh > epsr) then
           zeta = (rho (k, 1) - rho (k, 2) ) / rh
           call gcc_spin (rh, zeta, grh2, sc, v1cup, v1cdw, v2c)
           dvxc_rr (k, 1, 1) = e2 * (vrrxup + vrrcup + vrzcup * &
                (1.d0 - zeta) / rh)
           dvxc_rr (k, 1, 2) = e2 * (vrrcup - vrzcup * (1.d0 + zeta) / rh)
           dvxc_rr (k, 2, 1) = e2 * (vrrcdw + vrzcdw * (1.d0 - zeta) / rh)
           dvxc_rr (k, 2, 2) = e2 * (vrrxdw + vrrcdw - vrzcdw * &
                (1.d0 + zeta) / rh)
           dvxc_s (k, 1, 1) = e2 * (v2xup + v2c)
           dvxc_s (k, 1, 2) = e2 * v2c
           dvxc_s (k, 2, 1) = e2 * v2c
           dvxc_s (k, 2, 2) = e2 * (v2xdw + v2c)
        else
           dvxc_rr (k, 1, 1) = 0.d0
           dvxc_rr (k, 1, 2) = 0.d0
           dvxc_rr (k, 2, 1) = 0.d0
           dvxc_rr (k, 2, 2) = 0.d0
           dvxc_s (k, 1, 1) = 0.d0
           dvxc_s (k, 1, 2) = 0.d0
           dvxc_s (k, 2, 1) = 0.d0
           dvxc_s (k, 2, 2) = 0.d0
        endif
        dvxc_sr (k, 1, 1) = e2 * (vrsxup + vrscup)
        dvxc_sr (k, 1, 2) = e2 * vrscup
        dvxc_sr (k, 2, 1) = e2 * vrscdw
        dvxc_sr (k, 2, 2) = e2 * (vrsxdw + vrscdw)
        dvxc_ss (k, 1, 1) = e2 * (vssxup + vssc)
        dvxc_ss (k, 1, 2) = e2 * vssc
        dvxc_ss (k, 2, 1) = e2 * vssc
        dvxc_ss (k, 2, 2) = e2 * (vssxdw + vssc)
     endif
  enddo
  if (nlcc_any) then
     do is = 1, nspin
        do k = 1, nrxx
           rho (k, is) = rho (k, is) - rho_core (k) * fac
        enddo
     enddo
  endif

  return
end subroutine setup_dgc