QuAcK/src/GT/GTpp_ppBSE_static_kernel_C.f90

subroutine GTpp_ppBSE_static_kernel_C(ispin,eta,nBas,nC,nO,nV,nR,nOO,nVV,nOOx,nVVx,lambda,Om1,rho1,Om2,rho2,TC)

! Compute the VVVV block of the static T-matrix

  implicit none
  include 'parameters.h'

! Input variables

  integer,intent(in)            :: ispin
  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)            :: nOO
  integer,intent(in)            :: nVV
  integer,intent(in)            :: nOOx
  integer,intent(in)            :: nVVx
  double precision,intent(in)   :: lambda
  double precision,intent(in)   :: Om1(nVV)
  double precision,intent(in)   :: rho1(nBas,nBas,nVV)
  double precision,intent(in)   :: Om2(nOO)
  double precision,intent(in)   :: rho2(nBas,nBas,nOO)

! Local variables

  double precision,external     :: Kronecker_delta
  double precision              :: chi
  double precision              :: eps
  integer                       :: a,b,c,d,ab,cd,ef,mn

! Output variables

  double precision,intent(out)  :: TC(nVVx,nVVx)

!===============!
! singlet block !
!===============!

  if(ispin == 1) then

    ab = 0
    do a=nO+1,nBas-nR
      do b=a,nBas-nR
        ab = ab + 1

        cd = 0
        do c=nO+1,nBas-nR
          do d=c,nBas-nR
            cd = cd + 1
 
            chi = 0d0
 
            do ef=1,nVV
              eps = + Om1(ef)
              chi = chi + rho1(a,b,ef)*rho1(c,d,ef)*eps/(eps**2 + eta**2) &
                        + rho1(a,b,ef)*rho1(d,c,ef)*eps/(eps**2 + eta**2)
            end do
 
            do mn=1,nOO
              eps = - Om2(mn)
              chi = chi + rho2(a,b,mn)*rho2(c,d,mn)*eps/(eps**2 + eta**2) &
                        + rho2(a,b,mn)*rho2(d,c,mn)*eps/(eps**2 + eta**2)
            end do
 
            TC(ab,cd) = 0.5d0*lambda*chi/sqrt((1d0 + Kronecker_delta(a,b))*(1d0 + Kronecker_delta(c,d)))
 
          end do
        end do

      end do
    end do

  end if

!===============!
! triplet block !
!===============!

  if(ispin == 2 .or. ispin == 4) then

    ab = 0
    do a=nO+1,nBas-nR
      do b=a+1,nBas-nR
        ab = ab + 1

        cd = 0
        do c=nO+1,nBas-nR
          do d=c+1,nBas-nR
            cd = cd + 1
 
            chi = 0d0
 
            do ef=1,nVV
              eps = + Om1(ef)
              chi = chi + rho1(a,b,ef)*rho1(c,d,ef)*eps/(eps**2 + eta**2)
            end do
 
            do mn=1,nOO
              eps = - Om2(mn)
              chi = chi + rho2(a,b,mn)*rho2(c,d,mn)*eps/(eps**2 + eta**2)
            end do
 
            TC(ab,cd) = lambda*chi
 
          end do
        end do

      end do
    end do

  end if

!==================!
! alpha-beta block !
!==================!

  if(ispin == 3) then

    ab = 0
    do a=nO+1,nBas-nR
      do b=nO+1,nBas-nR
        ab = ab + 1

        cd = 0
        do c=nO+1,nBas-nR
          do d=nO+1,nBas-nR
            cd = cd + 1

            chi = 0d0
 
            do ef=1,nVV
              eps = + Om1(ef)
              chi = chi + rho1(a,b,ef)*rho1(c,d,ef)*eps/(eps**2 + eta**2)
            end do
 
            do mn=1,nOO
              eps = - Om2(mn)
              chi = chi + rho2(a,b,mn)*rho2(c,d,mn)*eps/(eps**2 + eta**2)
            end do
 
            TC(ab,cd) = lambda*chi
 
          end do
        end do

      end do
    end do

  end if

end subroutine