2020-03-28 22:52:45 +01:00
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subroutine RB88_gga_exchange_potential(nGrid,weight,nBas,AO,dAO,rho,drho,Fx)
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! Compute restricted 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(ncart,nBas,nGrid)
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double precision,intent(in) :: rho(nGrid)
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double precision,intent(in) :: drho(ncart,nGrid)
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! Local variables
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integer :: mu,nu,iG
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double precision :: alpha
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double precision :: beta
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double precision :: r,g,vAO,gAO
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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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alpha = -(3d0/2d0)*(3d0/(4d0*pi))**(1d0/3d0)
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beta = 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(0d0,0.5d0*rho(iG))
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if(r > threshold) then
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2020-04-06 22:27:13 +02:00
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g = 0.25d0*(drho(1,iG)**2 + drho(2,iG)**2 + drho(3,iG)**2)
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2020-03-28 22:52:45 +01:00
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vAO = weight(iG)*AO(mu,iG)*AO(nu,iG)
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Fx(mu,nu) = Fx(mu,nu) &
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+ vAO*(4d0/3d0*r**(1d0/3d0)*(alpha - beta*g**(3d0/4d0)/r**2) &
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+ 2d0*beta*g**(3d0/4d0)/r**(5d0/3d0))
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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*3d0/4d0*beta*g**(-1d0/4d0)/r**(2d0/3d0)
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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 RB88_gga_exchange_potential
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