quack/src/GF/BSE2.f90

subroutine BSE2(TDA,dBSE,dTDA,evDyn,singlet,triplet,eta,nBas,nC,nO,nV,nR,nS,ERI,dipole_int,eHF,eGF,EcBSE)

! Compute the second-order Bethe-Salpeter excitation energies

  implicit none
  include 'parameters.h'

! Input variables

  logical,intent(in)            :: TDA
  logical,intent(in)            :: dBSE
  logical,intent(in)            :: dTDA
  logical,intent(in)            :: evDyn
  logical,intent(in)            :: singlet
  logical,intent(in)            :: triplet

  double precision,intent(in)   :: eta
  integer,intent(in)            :: nBas
  integer,intent(in)            :: nC
  integer,intent(in)            :: nO
  integer,intent(in)            :: nV
  integer,intent(in)            :: nR
  integer,intent(in)            :: nS
  double precision,intent(in)   :: eHF(nBas)
  double precision,intent(in)   :: eGF(nBas)
  double precision,intent(in)   :: ERI(nBas,nBas,nBas,nBas)
  double precision,intent(in)   :: dipole_int(nBas,nBas,ncart)

! Local variables

  integer                       :: ispin
  double precision,allocatable  :: OmBSE(:,:)
  double precision,allocatable  :: XpY(:,:,:)
  double precision,allocatable  :: XmY(:,:,:)
  double precision              :: rho
  double precision,allocatable  :: A_sta(:,:,:)
  double precision,allocatable  :: B_sta(:,:,:)

! Output variables

  double precision,intent(out)  :: EcBSE(nspin)

! Memory allocation

  allocate(OmBSE(nS,nspin),XpY(nS,nS,nspin),XmY(nS,nS,nspin), &
           A_sta(nS,nS,nspin),B_sta(nS,nS,nspin))

!-------------------
! Singlet manifold
!-------------------

 if(singlet) then

    ispin = 1
    EcBSE(ispin) = 0d0

    ! Compute static kernel

                 call BSE2_A_matrix_static(ispin,eta,nBas,nC,nO,nV,nR,nS,1d0,ERI,eGF,A_sta(:,:,ispin))
    if(.not.TDA) call BSE2_B_matrix_static(ispin,eta,nBas,nC,nO,nV,nR,nS,1d0,ERI,eGF,B_sta(:,:,ispin))

    ! Compute BSE2 excitation energies

    call linear_response_BSE(ispin,.false.,TDA,.true.,eta,nBas,nC,nO,nV,nR,nS,1d0,eGF,ERI,-A_sta(:,:,ispin),-B_sta(:,:,ispin), &
                             EcBSE(ispin),OmBSE(:,ispin),XpY(:,:,ispin),XmY(:,:,ispin))
    call print_excitation('BSE2        ',ispin,nS,OmBSE(:,ispin))
    call print_transition_vectors(.true.,nBas,nC,nO,nV,nR,nS,dipole_int,OmBSE(:,ispin),XpY(:,:,ispin),XmY(:,:,ispin))


    ! Compute dynamic correction for BSE via perturbation theory

    if(dBSE) then

     if(evDyn) then

      call BSE2_dynamic_perturbation_iterative(dTDA,ispin,eta,nBas,nC,nO,nV,nR,nS,ERI,dipole_int,eHF,eGF, & 
                                               A_sta(:,:,ispin),B_sta(:,:,ispin),OmBSE(:,ispin),XpY(:,:,ispin),XmY(:,:,ispin))
     else
 
      call BSE2_dynamic_perturbation(dTDA,ispin,eta,nBas,nC,nO,nV,nR,nS,ERI,dipole_int,eHF,eGF, & 
                                     A_sta(:,:,ispin),B_sta(:,:,ispin),OmBSE(:,ispin),XpY(:,:,ispin),XmY(:,:,ispin))
 
      end if

    end if

  end if

!-------------------
! Triplet manifold
!-------------------

 if(triplet) then

    ispin = 2
    EcBSE(ispin) = 0d0

    ! Compute static kernel

                 call BSE2_A_matrix_static(ispin,eta,nBas,nC,nO,nV,nR,nS,1d0,ERI,eGF,A_sta(:,:,ispin))
    if(.not.TDA) call BSE2_B_matrix_static(ispin,eta,nBas,nC,nO,nV,nR,nS,1d0,ERI,eGF,B_sta(:,:,ispin))

    ! Compute BSE2 excitation energies

    call linear_response_BSE(ispin,.false.,TDA,.true.,eta,nBas,nC,nO,nV,nR,nS,1d0,eGF,ERI,-A_sta(:,:,ispin),-B_sta(:,:,ispin), &
                             EcBSE(ispin),OmBSE(:,ispin),XpY(:,:,ispin),XmY(:,:,ispin))
    call print_excitation('BSE2        ',ispin,nS,OmBSE(:,ispin))
    call print_transition_vectors(.false.,nBas,nC,nO,nV,nR,nS,dipole_int,OmBSE(:,ispin),XpY(:,:,ispin),XmY(:,:,ispin))

    ! Compute dynamic correction for BSE via perturbation theory

    if(dBSE) then

     if(evDyn) then

      call BSE2_dynamic_perturbation_iterative(dTDA,ispin,eta,nBas,nC,nO,nV,nR,nS,ERI,dipole_int,eHF,eGF, & 
                                               A_sta(:,:,ispin),B_sta(:,:,ispin),OmBSE(:,ispin),XpY(:,:,ispin),XmY(:,:,ispin))
     else
 
      call BSE2_dynamic_perturbation(dTDA,ispin,eta,nBas,nC,nO,nV,nR,nS,ERI,dipole_int,eHF,eGF, &
                                     A_sta(:,:,ispin),B_sta(:,:,ispin),OmBSE(:,ispin),XpY(:,:,ispin),XmY(:,:,ispin))
 
      end if

    end if

  end if

end subroutine BSE2