2020-03-28 22:52:45 +01:00
|
|
|
subroutine RB88_gga_exchange_energy(nGrid,weight,rho,drho,Ex)
|
|
|
|
|
|
|
|
|
|
! Compute restricted version of Becke's 88 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,x
|
|
|
|
|
|
|
|
|
|
! Output variables
|
|
|
|
|
|
|
|
|
|
double precision :: Ex
|
|
|
|
|
|
|
|
|
|
! Coefficients for B88 GGA exchange functional
|
|
|
|
|
|
|
|
|
|
beta = 0.0042d0
|
|
|
|
|
|
|
|
|
|
! Compute GGA exchange energy
|
|
|
|
|
|
|
|
|
|
Ex = 0d0
|
|
|
|
|
|
|
|
|
|
do iG=1,nGrid
|
|
|
|
|
|
|
|
|
|
r = max(0d0,0.5d0*rho(iG))
|
|
|
|
|
|
|
|
|
|
if(r > threshold) then
|
2020-04-06 22:27:13 +02:00
|
|
|
g = 0.25d0*(drho(1,iG)**2 + drho(2,iG)**2 + drho(3,iG)**2)
|
2020-03-28 22:52:45 +01:00
|
|
|
x = sqrt(g)/r**(4d0/3d0)
|
|
|
|
|
|
2021-02-15 17:27:06 +01:00
|
|
|
Ex = Ex + weight(iG)*CxLDA*r**(4d0/3d0) &
|
2020-03-28 22:52:45 +01:00
|
|
|
- weight(iG)*beta*x**2*r**(4d0/3d0)/(1d0 + 6d0*beta*x*asinh(x))
|
|
|
|
|
|
|
|
|
|
end if
|
|
|
|
|
|
|
|
|
|
end do
|
|
|
|
|
|
|
|
|
|
Ex = 2d0*Ex
|
|
|
|
|
|
|
|
|
|
end subroutine RB88_gga_exchange_energy
|
