2020-01-17 15:31:38 +01:00
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subroutine ACFDT_correlation_energy(ispin,exchange_kernel,nBas,nC,nO,nV,nR,nS,ERI,XpY,XmY,EcAC)
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! Compute the correlation energy via the adiabatic connection formula
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implicit none
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include 'parameters.h'
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! Input variables
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integer,intent(in) :: ispin
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logical,intent(in) :: exchange_kernel
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integer,intent(in) :: nBas,nC,nO,nV,nR,nS
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double precision,intent(in) :: ERI(nBas,nBas,nBas,nBas)
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double precision,intent(in) :: XpY(nS,nS)
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double precision,intent(in) :: XmY(nS,nS)
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! Local variables
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integer :: i,j,a,b
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integer :: ia,jb,kc
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double precision :: delta_spin
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double precision :: delta_Kx
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double precision,allocatable :: Ap(:,:)
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double precision,allocatable :: Bp(:,:)
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double precision,allocatable :: X(:,:)
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double precision,allocatable :: Y(:,:)
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double precision,external :: trace_matrix
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! Output variables
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double precision,intent(out) :: EcAC
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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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! Exchange kernel
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delta_Kx = 0d0
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if(exchange_kernel) delta_Kx = 1d0
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! Memory allocation
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2020-01-25 15:49:09 +01:00
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allocate(Ap(nS,nS),Bp(nS,nS),X(nS,nS),Y(nS,nS))
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2020-01-17 15:31:38 +01:00
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! Compute Aiajb = (ia|bj) and Biajb = (ia|jb)
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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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Ap(ia,jb) = (1d0 + delta_spin)*ERI(i,b,a,j) &
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- delta_Kx*ERI(i,b,j,a)
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Bp(ia,jb) = (1d0 + delta_spin)*ERI(i,j,a,b) &
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- delta_Kx*ERI(i,j,b,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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! Compute Tr(K x P_lambda)
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2020-06-14 20:51:02 +02:00
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X(:,:) = 0.5d0*(XpY(:,:) + XmY(:,:))
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Y(:,:) = 0.5d0*(XpY(:,:) - XmY(:,:))
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2020-01-17 15:31:38 +01:00
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EcAC = trace_matrix(nS,matmul(X,matmul(Bp,transpose(Y))) + matmul(Y,matmul(Bp,transpose(X)))) &
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+ trace_matrix(nS,matmul(X,matmul(Ap,transpose(X))) + matmul(Y,matmul(Ap,transpose(Y)))) &
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- trace_matrix(nS,Ap)
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end subroutine ACFDT_correlation_energy
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