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https://github.com/pfloos/quack
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76 lines
1.5 KiB
Fortran
76 lines
1.5 KiB
Fortran
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subroutine RCC_lda_exchange_energy(nEns,wEns,nGrid,weight,rho,Ex)
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! Compute the restricted version of the curvature-corrected exchange functional
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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) :: nEns
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double precision,intent(in) :: wEns(nEns)
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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)
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! Local variables
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integer :: iG
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double precision :: r
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double precision :: a1,b1,c1,w1
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double precision :: a2,b2,c2,w2
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double precision :: Fx1,Fx2,Cx
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! Output variables
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double precision :: Ex
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! Single excitation parameter
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a1 = 0.0d0
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b1 = 0.0d0
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c1 = 0.0d0
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! Parameters for H2 at equilibrium
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! a2 = +0.5751782560799208d0
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! b2 = -0.021108186591137282d0
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! c2 = -0.36718902716347124d0
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! Parameters for stretch H2
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a2 = + 0.01922622507087411d0
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b2 = - 0.01799647558018601d0
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c2 = - 0.022945430666782573d0
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! Parameters for He
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! a2 = 1.9125735895875828d0
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! b2 = 2.715266992840757d0
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! c2 = 2.1634223380633086d0
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w1 = wEns(2)
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Fx1 = 1d0 - w1*(1d0 - w1)*(a1 + b1*(w1 - 0.5d0) + c1*(w1 - 0.5d0)**2)
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w2 = wEns(3)
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Fx2 = 1d0 - w2*(1d0 - w2)*(a2 + b2*(w2 - 0.5d0) + c2*(w2 - 0.5d0)**2)
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Cx = CxLDA*Fx1*Fx2
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! Compute GIC-LDA exchange energy
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Ex = 0d0
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do iG=1,nGrid
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r = max(0d0,rho(iG))
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if(r > threshold) then
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Ex = Ex + weight(iG)*Cx*r**(4d0/3d0)
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endif
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enddo
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end subroutine RCC_lda_exchange_energy
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