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QuAcK/src/eDFT/fock_exchange_individual_energy.f90

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subroutine fock_exchange_individual_energy(nBas,Pw,P,ERI,Ex)
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! Compute the Fock exchange potential
implicit none
! Input variables
integer,intent(in) :: nBas
double precision,intent(in) :: Pw(nBas,nBas)
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double precision,intent(in) :: P(nBas,nBas)
double precision,intent(in) :: ERI(nBas,nBas,nBas,nBas)
! Local variables
integer :: mu,nu,la,si
double precision,allocatable :: Fx(:,:)
double precision,external :: trace_matrix
! Output variables
double precision,intent(out) :: Ex
! Compute HF exchange matrix
allocate(Fx(nBas,nBas))
Fx(:,:) = 0d0
do si=1,nBas
do la=1,nBas
do nu=1,nBas
do mu=1,nBas
Fx(mu,nu) = Fx(mu,nu) + P(la,si)*ERI(mu,la,si,nu)
enddo
enddo
enddo
enddo
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Ex = -0.25d0*trace_matrix(nBas,matmul(P(:,:),Fx(:,:)))
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end subroutine fock_exchange_individual_energy