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QuAcK/src/eDFT/UCC_lda_exchange_energy.f90

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subroutine UCC_lda_exchange_energy(nEns,wEns,aCC_w1,aCC_w2,nGrid,weight,rho,Ex,Cx_choice)
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! 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)
double precision,intent(in) :: aCC_w1(3)
double precision,intent(in) :: aCC_w2(3)
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integer,intent(in) :: nGrid
double precision,intent(in) :: weight(nGrid)
double precision,intent(in) :: rho(nGrid)
integer,intent(in) :: Cx_choice
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! Local variables
integer :: iG
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double precision :: r
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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 = aCC_w1(1)
b1 = aCC_w1(2)
c1 = aCC_w1(3)
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! Parameters for He N -> N+1
a2 = aCC_w2(1)
b2 = aCC_w2(2)
c2 = aCC_w2(3)
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! 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)
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w2 = wEns(3)
Fx2 = 1d0 - w2*(1d0 - w2)*(a2 + b2*(w2 - 0.5d0) + c2*(w2 - 0.5d0)**2)
select case (Cx_choice)
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case(1)
Cx = CxLSDA*Fx1
case(2)
Cx = CxLSDA*Fx2
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case(3)
Cx = CxLSDA*Fx2*Fx1
case default
Cx = CxLSDA
end select
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! 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