mirror of
https://github.com/pfloos/quack
synced 2024-09-01 17:13:45 +02:00
49 lines
931 B
Fortran
49 lines
931 B
Fortran
subroutine UG96_gga_exchange_energy(nGrid,weight,rho,drho,Ex)
|
|
|
|
! Compute Gill's 96 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(ncart,nGrid)
|
|
|
|
! Local variables
|
|
|
|
integer :: iG
|
|
double precision :: beta
|
|
double precision :: r,g
|
|
|
|
! Output variables
|
|
|
|
double precision :: Ex
|
|
|
|
! Coefficients for G96 GGA exchange functional
|
|
|
|
beta = 1d0/137d0
|
|
|
|
! 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
|
|
|
|
Ex = Ex + weight(iG)*r**(4d0/3d0)*(CxLSDA - beta*g**(3d0/4d0)/r**2)
|
|
|
|
end if
|
|
|
|
end do
|
|
|
|
end subroutine UG96_gga_exchange_energy
|