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https://github.com/pfloos/quack
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74 lines
2.1 KiB
Fortran
74 lines
2.1 KiB
Fortran
subroutine UB88_gga_exchange_potential(nGrid,weight,nBas,AO,dAO,rho,drho,Fx)
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! Compute Becke's GGA exchange potential
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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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integer,intent(in) :: nBas
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double precision,intent(in) :: AO(nBas,nGrid)
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double precision,intent(in) :: dAO(3,nBas,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 :: mu,nu,iG
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double precision :: b
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double precision :: vAO,gAO
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double precision :: r,g,x,dxdr,dxdg,f
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! Output variables
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double precision,intent(out) :: Fx(nBas,nBas)
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! Coefficients for B88 GGA exchange functional
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b = 0.0042d0
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! Compute GGA exchange matrix in the AO basis
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Fx(:,:) = 0d0
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do mu=1,nBas
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do nu=1,nBas
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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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vAO = weight(iG)*AO(mu,iG)*AO(nu,iG)
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g = drho(1,iG)**2 + drho(2,iG)**2 + drho(3,iG)**2
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x = sqrt(g)/r**(4d0/3d0)
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dxdr = - 4d0*sqrt(g)/(3d0*r**(7d0/3d0))/x
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dxdg = + 1d0/(2d0*sqrt(g)*r**(4d0/3d0))/x
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f = b*x**2/(1d0 + 6d0*b*x*asinh(x))
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Fx(mu,nu) = Fx(mu,nu) + vAO*( &
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4d0/3d0*r**(1d0/3d0)*(CxLSDA - f) &
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- 2d0*r**(4d0/3d0)*dxdr*f &
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+ r**(4d0/3d0)*dxdr*(6d0*b*x*asinh(x) + 6d0*b*x**2/sqrt(1d0+x**2))*f/(1d0 + 6d0*b*x*asinh(x)) )
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gAO = drho(1,iG)*(dAO(1,mu,iG)*AO(nu,iG) + AO(mu,iG)*dAO(1,nu,iG)) &
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+ drho(2,iG)*(dAO(2,mu,iG)*AO(nu,iG) + AO(mu,iG)*dAO(2,nu,iG)) &
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+ drho(3,iG)*(dAO(3,mu,iG)*AO(nu,iG) + AO(mu,iG)*dAO(3,nu,iG))
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gAO = weight(iG)*gAO
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Fx(mu,nu) = Fx(mu,nu) + 2d0*gAO*r**(4d0/3d0)*dxdg*( &
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- 2d0*f + (6d0*b*x*asinh(x) + 6d0*b*x**2/sqrt(1d0+x**2))*f/(1d0 + 6d0*b*x*asinh(x)) )
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end if
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end do
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end do
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end do
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end subroutine UB88_gga_exchange_potential
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