mirror of
https://github.com/pfloos/quack
synced 2024-12-26 14:23:38 +01:00
53 lines
950 B
Fortran
53 lines
950 B
Fortran
|
subroutine W38_lda_correlation_energy(nGrid,weight,rho,Ec)
|
||
|
|
|
||
|
|
! Compute Wigner's LDA correlation energy
|
||
|
|
|
||
|
|
implicit none
|
||
|
|
include 'parameters.h'
|
||
|
|
|
||
|
|
! Input variables
|
||
|
|
|
||
|
|
integer,intent(in) :: nGrid
|
||
|
|
double precision,intent(in) :: weight(nGrid)
|
||
|
|
double precision,intent(in) :: rho(nGrid,nspin)
|
||
|
|
|
||
|
|
! Local variables
|
||
|
|
|
||
|
|
integer :: iG
|
||
|
|
double precision :: ra,rb,r
|
||
|
|
double precision :: a,d,epsc
|
||
|
|
|
||
|
|
! Output variables
|
||
|
|
|
||
|
|
double precision :: Ec(nsp)
|
||
|
|
|
||
|
|
! Coefficients for Wigner's LDA correlation
|
||
|
|
|
||
|
|
a = 0.04918d0
|
||
|
|
d = 0.349d0
|
||
|
|
|
||
|
|
! Compute LDA correlation energy
|
||
|
|
|
||
|
|
Ec(:) = 0d0
|
||
|
|
|
||
|
|
do iG=1,nGrid
|
||
|
|
|
||
|
|
ra = max(0d0,rho(iG,1))
|
||
|
|
rb = max(0d0,rho(iG,2))
|
||
|
|
|
||
|
|
if(ra > threshold .and. rb > threshold) then
|
||
|
|
|
||
|
|
r = ra + rb
|
||
|
|
|
||
|
|
epsc = ra*rb/(r + d*r**(2d0/3d0))
|
||
|
|
|
||
|
|
Ec(2) = Ec(2) + weight(iG)*epsc
|
||
|
|
|
||
|
|
endif
|
||
|
|
|
||
|
|
enddo
|
||
|
|
|
||
|
|
Ec(2) = -4d0*a*Ec(2)
|
||
|
|
|
||
|
|
end subroutine W38_lda_correlation_energy
|