mirror of https://github.com/pfloos/quack
59 lines
1.3 KiB
Fortran
59 lines
1.3 KiB
Fortran
subroutine linear_response_A_matrix(ispin,dRPA,nBas,nC,nO,nV,nR,nS,lambda,e,ERI,A_lr)
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! Compute linear response
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implicit none
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include 'parameters.h'
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! Input variables
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logical,intent(in) :: dRPA
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integer,intent(in) :: ispin,nBas,nC,nO,nV,nR,nS
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double precision,intent(in) :: lambda
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double precision,intent(in) :: e(nBas)
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double precision,intent(in) :: ERI(nBas,nBas,nBas,nBas)
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! Local variables
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double precision :: delta_spin,delta_dRPA
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double precision :: Kronecker_delta
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integer :: i,j,a,b,ia,jb
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! Output variables
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double precision,intent(out) :: A_lr(nS,nS)
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! Singlet or triplet manifold?
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delta_spin = 0d0
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if(ispin == 1) delta_spin = +1d0
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if(ispin == 2) delta_spin = -1d0
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! Direct RPA
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delta_dRPA = 0d0
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if(dRPA) delta_dRPA = 1d0
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! Build A matrix
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ia = 0
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do i=nC+1,nO
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do a=nO+1,nBas-nR
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ia = ia + 1
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jb = 0
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do j=nC+1,nO
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do b=nO+1,nBas-nR
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jb = jb + 1
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A_lr(ia,jb) = (e(a) - e(i))*Kronecker_delta(i,j)*Kronecker_delta(a,b) &
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+ (1d0 + delta_spin)*lambda*ERI(i,b,a,j) &
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- (1d0 - delta_dRPA)*lambda*ERI(i,b,j,a)
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enddo
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enddo
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enddo
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enddo
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end subroutine linear_response_A_matrix
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