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63 lines
1.4 KiB
Fortran
63 lines
1.4 KiB
Fortran
subroutine UW38_lda_correlation_individual_energy(nGrid,weight,rhow,rho,Ec)
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! Compute the unrestricted version of the Wigner's LDA individual 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) :: rhow(nGrid,nspin)
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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 :: raI,rbI,rI
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double precision :: a,d,epsc
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double precision :: dFcdra,dFcdrb
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! Output variables
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double precision,intent(out) :: 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 individual energy
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Ec(:) = 0d0
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do iG=1,nGrid
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ra = max(0d0,rhow(iG,1))
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rb = max(0d0,rhow(iG,2))
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raI = max(0d0,rho(iG,1))
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rbI = max(0d0,rho(iG,2))
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r = ra + rb
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rI = raI + rbI
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if(r > threshold .or. rI > threshold) then
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epsc = ra*rb/(r + d*r**(2d0/3d0))
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dFcdra = epsc*(d/(3d0*r**(4d0/3d0)*(1d0 + d*r**(-1d0/3d0))) - 1d0/r + 1d0/ra)
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dFcdrb = epsc*(d/(3d0*r**(4d0/3d0)*(1d0 + d*r**(-1d0/3d0))) - 1d0/r + 1d0/rb)
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Ec(2) = Ec(2) + weight(iG)*rI*0.5d0*(dFcdra + dFcdrb)
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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 UW38_lda_correlation_individual_energy
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