mirror of https://github.com/pfloos/quack
91 lines
2.3 KiB
Fortran
91 lines
2.3 KiB
Fortran
subroutine phLR(TDA,nS,Aph,Bph,EcRPA,Om,XpY,XmY)
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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) :: TDA
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integer,intent(in) :: nS
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double precision,intent(in) :: Aph(nS,nS)
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double precision,intent(in) :: Bph(nS,nS)
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! Local variables
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double precision :: trace_matrix
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double precision,allocatable :: ApB(:,:)
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double precision,allocatable :: AmB(:,:)
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double precision,allocatable :: AmBSq(:,:)
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double precision,allocatable :: AmBIv(:,:)
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double precision,allocatable :: Z(:,:)
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double precision,allocatable :: tmp(:,:)
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! Output variables
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double precision,intent(out) :: EcRPA
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double precision,intent(out) :: Om(nS)
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double precision,intent(out) :: XpY(nS,nS)
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double precision,intent(out) :: XmY(nS,nS)
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! Memory allocation
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allocate(ApB(nS,nS),AmB(nS,nS),AmBSq(nS,nS),AmBIv(nS,nS),Z(nS,nS),tmp(nS,nS))
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! Tamm-Dancoff approximation
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if(TDA) then
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XpY(:,:) = Aph(:,:)
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call diagonalize_matrix(nS,XpY,Om)
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XpY(:,:) = transpose(XpY(:,:))
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XmY(:,:) = XpY(:,:)
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else
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ApB(:,:) = Aph(:,:) + Bph(:,:)
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AmB(:,:) = Aph(:,:) - Bph(:,:)
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! Diagonalize linear response matrix
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call diagonalize_matrix(nS,AmB,Om)
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if(minval(Om) < 0d0) &
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call print_warning('You may have instabilities in linear response: A-B is not positive definite!!')
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call ADAt(nS,AmB,1d0*dsqrt(Om),AmBSq)
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call ADAt(nS,AmB,1d0/dsqrt(Om),AmBIv)
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call dgemm('N','N',nS,nS,nS,1d0,ApB,size(ApB,1),AmBSq,size(AmBSq,1),0d0,tmp,size(tmp,1))
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call dgemm('N','N',nS,nS,nS,1d0,AmBSq,size(AmBSq,1),tmp,size(tmp,1),0d0,Z,size(Z,1))
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! Z = matmul(AmBSq,matmul(ApB,AmBSq))
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call diagonalize_matrix(nS,Z,Om)
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if(minval(Om) < 0d0) &
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call print_warning('You may have instabilities in linear response: negative excitations!!')
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Om = sqrt(Om)
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call dgemm('T','N',nS,nS,nS,1d0,Z,size(Z,1),AmBSq,size(AmBSq,1),0d0,XpY,size(XpY,1))
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call DA(nS,1d0/dsqrt(Om),XpY)
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call dgemm('T','N',nS,nS,nS,1d0,Z,size(Z,1),AmBIv,size(AmBIv,1),0d0,XmY,size(XmY,1))
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call DA(nS,1d0*dsqrt(Om),XmY)
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! XpY = matmul(transpose(Z),AmBSq)
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! call DA(nS,1d0/sqrt(Om),XpY)
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! XmY = matmul(transpose(Z),AmBIv)
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! call DA(nS,1d0*sqrt(Om),XmY)
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end if
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! Compute the RPA correlation energy
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EcRPA = 0.5d0*(sum(Om) - trace_matrix(nS,Aph))
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end subroutine
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