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https://github.com/pfloos/quack
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77 lines
1.7 KiB
Fortran
77 lines
1.7 KiB
Fortran
subroutine W38_lda_correlation_potential(nGrid,weight,nBas,AO,rho,Fc)
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! Compute the unrestricted version of the Wigner's LDA correlation potential
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implicit none
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include 'parameters.h'
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! Input variables
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integer,intent(in) :: nGrid
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double precision,intent(in) :: weight(nGrid)
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integer,intent(in) :: nBas
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double precision,intent(in) :: AO(nBas,nGrid)
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double precision,intent(in) :: rho(nGrid,nspin)
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! Local variables
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integer :: mu,nu,iG
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double precision :: ra,rb,r
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double precision :: a,d,ec
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double precision :: dFcdr
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! Output variables
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double precision,intent(out) :: Fc(nBas,nBas,nspin)
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! Coefficients for Wigner's LDA correlation
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a = 0.04918d0
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d = 0.349d0
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! Compute LDA correlation matrix in the AO basis
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Fc(:,:,:) = 0d0
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do mu=1,nBas
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do nu=1,nBas
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do iG=1,nGrid
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ra = max(0d0,rho(iG,1))
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rb = max(0d0,rho(iG,2))
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! Spin-up part contribution
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if(ra > threshold) then
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r = ra + rb
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ec = ra*rb/(r + d*r**(2d0/3d0))
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dFcdr = ec*(d/(3d0*r**(4d0/3d0)*(1d0 + d*r**(-1d0/3d0))) - 1d0/r + 1d0/ra)
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Fc(mu,nu,1) = Fc(mu,nu,1) + weight(iG)*AO(mu,iG)*AO(nu,iG)*dFcdr
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endif
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! Spin-down part contribution
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if(rb > threshold) then
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r = ra + rb
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ec = ra*rb/(r + d*r**(2d0/3d0))
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dFcdr = ec*(d/(3d0*r**(4d0/3d0)*(1d0 + d*r**(-1d0/3d0))) - 1d0/r + 1d0/rb)
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Fc(mu,nu,2) = Fc(mu,nu,2) + weight(iG)*AO(mu,iG)*AO(nu,iG)*dFcdr
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endif
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enddo
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enddo
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enddo
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Fc(:,:,:) = -4d0*a*Fc(:,:,:)
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end subroutine W38_lda_correlation_potential
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