mirror of
https://github.com/pfloos/quack
synced 2024-11-19 12:32:36 +01:00
94 lines
1.8 KiB
Fortran
94 lines
1.8 KiB
Fortran
subroutine UC16_lda_correlation_energy(nGrid,weight,rho,Ec)
|
|
|
|
! Compute unrestricted Chachiyo'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,rs
|
|
double precision :: a_p,b_p,ec_p
|
|
double precision :: a_f,b_f,ec_f
|
|
double precision :: z,fz,ec_z
|
|
|
|
! Output variables
|
|
|
|
double precision :: Ec(nsp)
|
|
|
|
! Coefficients for Chachiyo's LDA correlation
|
|
|
|
a_p = (log(2d0) - 1d0)/(2d0*pi**2)
|
|
b_p = 20.4562557d0
|
|
|
|
a_f = (log(2d0) - 1d0)/(4d0*pi**2)
|
|
b_f = 27.4203609d0
|
|
|
|
! Compute LDA correlation energy
|
|
|
|
Ec(:) = 0d0
|
|
|
|
do iG=1,nGrid
|
|
|
|
! Spin-up and spin-down densities
|
|
|
|
ra = max(0d0,rho(iG,1))
|
|
rb = max(0d0,rho(iG,2))
|
|
|
|
! Total density
|
|
|
|
r = ra + rb
|
|
|
|
! Spin-up part contribution
|
|
|
|
if(ra > threshold) then
|
|
|
|
rs = (4d0*pi*ra/3d0)**(-1d0/3d0)
|
|
ec_f = a_f*log(1d0 + b_f/rs + b_f/rs**2)
|
|
|
|
Ec(1) = Ec(1) + weight(iG)*ec_f*ra
|
|
|
|
endif
|
|
|
|
! Opposite-spin contribution
|
|
|
|
if(r > threshold) then
|
|
|
|
rs = (4d0*pi*r/3d0)**(-1d0/3d0)
|
|
ec_p = a_p*log(1d0 + b_p/rs + b_p/rs**2)
|
|
ec_f = a_f*log(1d0 + b_f/rs + b_f/rs**2)
|
|
|
|
z = (ra-rb)/r
|
|
fz = (1d0 + z)**(4d0/3d0) + (1d0 - z)**(4d0/3d0) - 2d0
|
|
fz = fz/(2d0*(2d0**(1d0/3d0) - 1d0))
|
|
|
|
ec_z = ec_p + (ec_f - ec_p)*fz
|
|
|
|
Ec(2) = Ec(2) + weight(iG)*ec_z*r
|
|
|
|
endif
|
|
|
|
! Spin-down contribution
|
|
|
|
if(rb > threshold) then
|
|
|
|
rs = (4d0*pi*rb/3d0)**(-1d0/3d0)
|
|
ec_f = a_f*log(1d0 + b_f/rs + b_f/rs**2)
|
|
|
|
Ec(3) = Ec(3) + weight(iG)*ec_f*rb
|
|
|
|
endif
|
|
|
|
enddo
|
|
|
|
Ec(2) = Ec(2) - Ec(1) - Ec(3)
|
|
|
|
end subroutine UC16_lda_correlation_energy
|