mirror of https://github.com/pfloos/quack
99 lines
2.2 KiB
Fortran
99 lines
2.2 KiB
Fortran
subroutine linear_response(ispin,dRPA,TDA,BSE,nBas,nC,nO,nV,nR,nS,lambda,e,ERI,rho,EcRPA,Omega,XpY)
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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,TDA,BSE
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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) :: rho(nBas,nBas,nS)
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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 :: trace_matrix
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double precision,allocatable :: A(:,:),B(:,:),ApB(:,:),AmB(:,:),AmBSq(:,:),Z(:,:)
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! Output variables
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double precision,intent(out) :: EcRPA
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double precision,intent(out) :: Omega(nS),XpY(nS,nS)
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! Memory allocation
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allocate(A(nS,nS),B(nS,nS),ApB(nS,nS),AmB(nS,nS),AmBSq(nS,nS),Z(nS,nS))
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! Build A and B matrices
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call linear_response_A_matrix(ispin,dRPA,nBas,nC,nO,nV,nR,nS,lambda,e,ERI,A)
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if(BSE) call Bethe_Salpeter_A_matrix(nBas,nC,nO,nV,nR,nS,lambda,ERI,Omega,rho,A)
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! Tamm-Dancoff approximation
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B = 0d0
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if(.not. TDA) then
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call linear_response_B_matrix(ispin,dRPA,nBas,nC,nO,nV,nR,nS,lambda,ERI,B)
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if(BSE) call Bethe_Salpeter_B_matrix(nBas,nC,nO,nV,nR,nS,lambda,ERI,Omega,rho,B)
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endif
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! Build A + B and A - B matrices
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ApB = A + B
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AmB = A - B
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! print*,'A'
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! call matout(nS,nS,A)
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! print*,'B'
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! call matout(nS,nS,B)
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! print*,'A+B'
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! call matout(nS,nS,ApB)
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! print*,'A-B'
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! call matout(nS,nS,AmB)
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! Diagonalize TD-HF matrix
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call diagonalize_matrix(nS,AmB,Omega)
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if(minval(Omega) < 0d0) &
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call print_warning('You may have instabilities in linear response!!')
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call ADAt(nS,AmB,sqrt(Omega),AmBSq)
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Z = matmul(AmBSq,matmul(ApB,AmBSq))
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! print*,'Z'
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! call matout(nS,nS,Z)
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call diagonalize_matrix(nS,Z,Omega)
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if(minval(Omega) < 0d0) &
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call print_warning('You may have instabilities in linear response!!')
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Omega = sqrt(Omega)
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XpY = matmul(transpose(Z),AmBSq)
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call DA(nS,1d0/sqrt(abs(Omega)),XpY)
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! print*,'X+Y'
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! call matout(nS,nS,XpY)
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! print*,'RPA excitations'
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! call matout(nS,1,Omega)
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! Compute the RPA correlation energy
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EcRPA = 0.5d0*(sum(Omega) - trace_matrix(nS,A))
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! print*,'EcRPA = ',EcRPA
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end subroutine linear_response
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