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https://github.com/pfloos/quack
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50 lines
1.0 KiB
Fortran
50 lines
1.0 KiB
Fortran
subroutine UPBE_gga_exchange_energy(nGrid,weight,rho,drho,Ex)
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! Compute PBE GGA 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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double precision,intent(in) :: drho(3,nGrid)
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! Local variables
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integer :: iG
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double precision :: mupbe,kappa
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double precision :: r,g,s2
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! Output variables
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double precision :: Ex
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! Coefficients for PBE exchange functional
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mupbe = ((1d0/2d0**(1d0/3d0))/(2d0*(3d0*pi**2)**(1d0/3d0)))**2*0.21951d0
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kappa = 0.804d0
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! Compute GGA 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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g = drho(1,iG)**2 + drho(2,iG)**2 + drho(3,iG)**2
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s2 = g/r**(8d0/3d0)
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Ex = Ex + weight(iG)*CxLSDA*r**(4d0/3d0)*(1d0 + kappa - kappa/(1d0 + mupbe*s2/kappa))
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end if
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end do
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end subroutine UPBE_gga_exchange_energy
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