mirror of
https://github.com/pfloos/quack
synced 2024-06-14 09:15:30 +02:00
50 lines
1.0 KiB
Fortran
50 lines
1.0 KiB
Fortran
subroutine UPBE_gga_exchange_energy(nGrid,weight,rho,drho,Ex)
|
|
|
|
! Compute PBE GGA exchange energy
|
|
|
|
implicit none
|
|
|
|
include 'parameters.h'
|
|
|
|
! Input variables
|
|
|
|
integer,intent(in) :: nGrid
|
|
double precision,intent(in) :: weight(nGrid)
|
|
double precision,intent(in) :: rho(nGrid)
|
|
double precision,intent(in) :: drho(3,nGrid)
|
|
|
|
! Local variables
|
|
|
|
integer :: iG
|
|
double precision :: mupbe,kappa
|
|
double precision :: r,g,s2
|
|
|
|
! Output variables
|
|
|
|
double precision :: Ex
|
|
|
|
! Coefficients for PBE exchange functional
|
|
|
|
mupbe = ((1d0/2d0**(1d0/3d0))/(2d0*(3d0*pi**2)**(1d0/3d0)))**2*0.21951d0
|
|
kappa = 0.804d0
|
|
|
|
! Compute GGA exchange energy
|
|
|
|
Ex = 0d0
|
|
|
|
do iG=1,nGrid
|
|
|
|
r = max(0d0,rho(iG))
|
|
|
|
if(r > threshold) then
|
|
g = drho(1,iG)**2 + drho(2,iG)**2 + drho(3,iG)**2
|
|
s2 = g/r**(8d0/3d0)
|
|
|
|
Ex = Ex + weight(iG)*CxLSDA*r**(4d0/3d0)*(1d0 + kappa - kappa/(1d0 + mupbe*s2/kappa))
|
|
|
|
end if
|
|
|
|
end do
|
|
|
|
end subroutine UPBE_gga_exchange_energy
|