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53 lines
981 B
Fortran
53 lines
981 B
Fortran
subroutine W38_lda_correlation_energy(nGrid,weight,rho,Ec)
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! Compute the unrestricted version of the Wigner's LDA correlation energy
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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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double precision,intent(in) :: rho(nGrid,nspin)
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! Local variables
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integer :: iG
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double precision :: ra,rb,r
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double precision :: a,d,epsc
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! Output variables
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double precision :: Ec(nsp)
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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 energy
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Ec(:) = 0d0
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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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if(ra > threshold .or. rb > threshold) then
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r = ra + rb
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epsc = ra*rb/(r + d*r**(2d0/3d0))
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Ec(2) = Ec(2) + weight(iG)*epsc
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endif
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enddo
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Ec(2) = -4d0*a*Ec(2)
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end subroutine W38_lda_correlation_energy
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