mirror of https://github.com/pfloos/quack
56 lines
1.1 KiB
Fortran
56 lines
1.1 KiB
Fortran
subroutine US51_lda_exchange_energy(nGrid,weight,rho,Ex)
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use xc_f90_lib_m
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! Compute Slater's LDA exchange 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)
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! Local variables
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integer :: iG
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double precision :: alpha,r,alphaw,a2,b2,c2,a1,b1,c1
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! Output variables
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double precision :: Ex
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! Cxw2 parameters for He N->N+1
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! a2 = 0.135068d0
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! b2 = -0.00774769d0
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! c2 = -0.0278205d0
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! Cxw1 parameters for He N->N-1
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! a1 = 0.420243d0
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! b1 = 0.0700561d0
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! c1 = -0.288301d0
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! Cx coefficient for Slater LDA exchange
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alpha = -(3d0/2d0)*(3d0/(4d0*pi))**(1d0/3d0)
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! alphaw = alpha*(1d0 - wEns(2)*(1d0 - wEns(2))*(a1 + b1*(wEns(2) - 0.5d0) + c1*(wEns(2) - 0.5d0)**2))
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! Compute 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)*alpha*r**(4d0/3d0)
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endif
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enddo
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end subroutine US51_lda_exchange_energy
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