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QuAcK/src/GW/static_screening_WC_pp.f90

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subroutine static_screening_WC_pp(ispin,eta,nBas,nC,nO,nV,nR,nS,nOO,nVV,lambda,ERI,Omega,rho,WC)
! Compute the VVVV block of the static screening W for the pp-BSE
implicit none
include 'parameters.h'
! Input variables
integer,intent(in) :: ispin
integer,intent(in) :: nBas
integer,intent(in) :: nC
integer,intent(in) :: nO
integer,intent(in) :: nV
integer,intent(in) :: nR
integer,intent(in) :: nS
integer,intent(in) :: nOO
integer,intent(in) :: nVV
double precision,intent(in) :: eta
double precision,intent(in) :: lambda
double precision,intent(in) :: ERI(nBas,nBas,nBas,nBas)
double precision,intent(in) :: Omega(nS)
double precision,intent(in) :: rho(nBas,nBas,nS)
! Local variables
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double precision,external :: Kronecker_delta
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double precision :: chi
double precision :: eps
integer :: a,b,c,d,ab,cd,m
! Output variables
double precision,intent(out) :: WC(nVV,nVV)
! Initialization
WC(:,:) = 0d0
!---------------!
! Singlet block !
!---------------!
if(ispin == 1) then
ab = 0
do a=nO+1,nBas-nR
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do b=a,nBas-nR
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ab = ab + 1
cd = 0
do c=nO+1,nBas-nR
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do d=c,nBas-nR
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cd = cd + 1
chi = 0d0
do m=1,nS
eps = Omega(m)**2 + eta**2
chi = chi + rho(a,c,m)*rho(b,d,m)*Omega(m)/eps &
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+ rho(a,d,m)*rho(b,c,m)*Omega(m)/eps
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enddo
WC(ab,cd) = + 4d0*lambda*chi/sqrt((1d0 + Kronecker_delta(a,b))*(1d0 + Kronecker_delta(c,d)))
end do
end do
end do
end do
end if
!---------------!
! Triplet block !
!---------------!
if(ispin == 2) then
ab = 0
do a=nO+1,nBas-nR
do b=a+1,nBas-nR
ab = ab + 1
cd = 0
do c=nO+1,nBas-nR
do d=c+1,nBas-nR
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cd = cd + 1
chi = 0d0
do m=1,nS
eps = Omega(m)**2 + eta**2
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chi = chi + rho(a,c,m)*rho(b,d,m)*Omega(m)/eps &
- rho(a,d,m)*rho(b,c,m)*Omega(m)/eps
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enddo
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WC(ab,cd) = + 4d0*lambda*chi
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end do
end do
end do
end do
end if
!---------------!
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! SpinOrb block !
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!---------------!
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if(ispin == 4) then
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ab = 0
do a=nO+1,nBas-nR
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do b=a+1,nBas-nR
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ab = ab + 1
cd = 0
do c=nO+1,nBas-nR
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do d=c+1,nBas-nR
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cd = cd + 1
chi = 0d0
do m=1,nS
eps = Omega(m)**2 + eta**2
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chi = chi + rho(a,c,m)*rho(b,d,m)*Omega(m)/eps &
- rho(a,d,m)*rho(b,c,m)*Omega(m)/eps
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enddo
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WC(ab,cd) = + 2d0*lambda*chi
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end do
end do
end do
end do
end if
end subroutine static_screening_WC_pp