!
! 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 delta_e (nr1, nr2, nr3, nrxx, rho, v_in, v_out, omega, &
 de, deband, nspin)
USE kinds
implicit none

integer :: nspin, nr1, nr2, nr3, nrxx, i, ipol
                             ! nspin=1 if LDA, nspin=2 if LSDA
                             ! fft grid dimensions
                             ! counters


real(kind=DP) :: rho (nrxx, nspin), v_in (nrxx, nspin), v_out (nrxx, &
 nspin), omega, de, deband
                             ! charge density
                             ! in and ...
                             ! ... out potentials from potential mixing
                             ! cell volume
                             ! total energy and band energy corrections
de = 0.d0
deband = 0.d0

if (nspin.ne.2) then
!
! LDA case
!
  do ipol=1,nspin
     do i = 1, nrxx
        de     = de + rho(i,ipol) * ( v_out(i,ipol) - v_in(i,ipol) )
        deband = deband - rho(i,ipol) * v_in(i,ipol)
     enddo
  enddo
else
!
! LSDA case
!
   do i = 1, nrxx
      de     = de + rho(i,1) * ( v_out(i,1) - v_in(i,1) ) + &
                    rho(i,2) * ( v_out(i,2) - v_in(i,2) )
      deband = deband - rho(i,1) * v_in(i,1) - rho(i,2) * v_in(i,2)
   enddo

endif

de = omega * de / (nr1 * nr2 * nr3)
deband = omega * deband / (nr1 * nr2 * nr3)

#ifdef __PARA
call reduce (1, de)
call reduce (1, deband)
#endif

return

end subroutine delta_e