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quack/src/eDFT/UCC_lda_exchange_energy.f90
2020-07-02 14:27:38 +02:00

95 lines
1.9 KiB
Fortran

subroutine UCC_lda_exchange_energy(nEns,wEns,nGrid,weight,rho,Ex)
! Compute the unrestricted version of the curvature-corrected exchange functional
implicit none
include 'parameters.h'
! Input variables
integer,intent(in) :: nEns
double precision,intent(in) :: wEns(nEns)
integer,intent(in) :: nGrid
double precision,intent(in) :: weight(nGrid)
double precision,intent(in) :: rho(nGrid)
! Local variables
integer :: iG
double precision :: r,alpha
double precision :: a1,b1,c1,w1
double precision :: a2,b2,c2,w2
double precision :: Fx1,Fx2,Cx
! Output variables
double precision :: Ex
! Single excitation parameter
! a1 = 0.0d0
! b1 = 0.0d0
! c1 = 0.0d0
! Parameters for H2 at equilibrium
! a2 = +0.5751782560799208d0
! b2 = -0.021108186591137282d0
! c2 = -0.36718902716347124d0
! Parameters for stretch H2
! a2 = + 0.01922622507087411d0
! b2 = - 0.01799647558018601d0
! c2 = - 0.022945430666782573d0
! Parameters for He
! a2 = 1.9125735895875828d0
! b2 = 2.715266992840757d0
! c2 = 2.1634223380633086d0
! Parameters for He N -> N-1
a1 = 0.420243d0
b1 = 0.0700561d0
c1 = -0.288301d0
! Parameters for He N -> N+1
a2 = 0.135068d0
b2 = -0.00774769d0
c2 = -0.0278205d0
! Cx coefficient for unrestricted Slater LDA exchange
alpha = -(3d0/2d0)*(3d0/(4d0*pi))**(1d0/3d0)
! Fx1 for states N and N-1
! Fx2 for states N and N+1
w1 = wEns(2)
Fx1 = 1d0 - w1*(1d0 - w1)*(a1 + b1*(w1 - 0.5d0) + c1*(w1 - 0.5d0)**2)
w2 = wEns(3)
Fx2 = 1d0 - w2*(1d0 - w2)*(a2 + b2*(w2 - 0.5d0) + c2*(w2 - 0.5d0)**2)
Cx = alpha*Fx2*Fx1
! Compute GIC-LDA exchange energy
Ex = 0d0
do iG=1,nGrid
r = max(0d0,rho(iG))
if(r > threshold) then
Ex = Ex + weight(iG)*Cx*r**(4d0/3d0)
endif
enddo
end subroutine UCC_lda_exchange_energy