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quack/src/QuAcK/Bethe_Salpeter_B_matrix.f90

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subroutine Bethe_Salpeter_B_matrix(eta,nBas,nC,nO,nV,nR,nS,lambda,ERI,Omega,rho,B_lr)
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! Compute the extra term for Bethe-Salpeter equation for linear response
implicit none
include 'parameters.h'
! Input variables
integer,intent(in) :: nBas,nC,nO,nV,nR,nS
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double precision,intent(in) :: eta
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double precision,intent(in) :: lambda
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double precision,intent(in) :: ERI(nBas,nBas,nBas,nBas)
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double precision,intent(in) :: Omega(nS)
double precision,intent(in) :: rho(nBas,nBas,nS)
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! Local variables
double precision :: chi
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double precision :: eps
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integer :: i,j,a,b,ia,jb,kc
! Output variables
double precision,intent(out) :: B_lr(nS,nS)
ia = 0
do i=nC+1,nO
do a=nO+1,nBas-nR
ia = ia + 1
jb = 0
do j=nC+1,nO
do b=nO+1,nBas-nR
jb = jb + 1
chi = 0d0
do kc=1,nS
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eps = Omega(kc)**2 + eta**2
chi = chi + rho(i,b,kc)*rho(a,j,kc)*Omega(kc)/eps
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enddo
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B_lr(ia,jb) = B_lr(ia,jb) - lambda*ERI(i,j,b,a) + 4d0*lambda*chi
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enddo
enddo
enddo
enddo
end subroutine Bethe_Salpeter_B_matrix