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QuAcK/src/MBPT/unrestricted_Bethe_Salpeter_B_matrix.f90

154 lines
3.8 KiB
Fortran

subroutine unrestricted_Bethe_Salpeter_B_matrix(ispin,eta,nBas,nC,nO,nV,nR,nSa,nSb,nSt,nS_sc,lambda, &
ERI_aaaa,ERI_aabb,ERI_bbbb,Omega,rho,B_lr)
! Compute the extra term for Bethe-Salpeter equation for linear response
implicit none
include 'parameters.h'
! Input variables
integer,intent(in) :: ispin
integer,intent(in) :: nBas
integer,intent(in) :: nC(nspin)
integer,intent(in) :: nO(nspin)
integer,intent(in) :: nV(nspin)
integer,intent(in) :: nR(nspin)
integer,intent(in) :: nSa
integer,intent(in) :: nSb
integer,intent(in) :: nSt
integer,intent(in) :: nS_sc
double precision,intent(in) :: eta
double precision,intent(in) :: lambda
double precision,intent(in) :: ERI_aaaa(nBas,nBas,nBas,nBas)
double precision,intent(in) :: ERI_aabb(nBas,nBas,nBas,nBas)
double precision,intent(in) :: ERI_bbbb(nBas,nBas,nBas,nBas)
double precision,intent(in) :: Omega(nS_sc)
double precision,intent(in) :: rho(nBas,nBas,nS_sc,nspin)
! Local variables
double precision :: chi
double precision :: eps
integer :: i,j,a,b,ia,jb,kc
! Output variables
double precision,intent(out) :: B_lr(nSt,nSt)
!--------------------------------------------------!
! Build BSE matrix for spin-conserving transitions !
!--------------------------------------------------!
if(ispin == 1) then
! aaaa block
ia = 0
do i=nC(1)+1,nO(1)
do a=nO(1)+1,nBas-nR(1)
ia = ia + 1
jb = 0
do j=nC(1)+1,nO(1)
do b=nO(1)+1,nBas-nR(1)
jb = jb + 1
chi = 0d0
do kc=1,nS_sc
eps = Omega(kc)**2 + eta**2
chi = chi + rho(i,b,kc,1)*rho(a,j,kc,1)*Omega(kc)/eps
enddo
B_lr(ia,jb) = B_lr(ia,jb) - lambda*ERI_aaaa(i,j,b,a) + 2d0*lambda*chi
enddo
enddo
enddo
enddo
! bbbb block
ia = 0
do i=nC(2)+1,nO(2)
do a=nO(2)+1,nBas-nR(2)
ia = ia + 1
jb = 0
do j=nC(2)+1,nO(2)
do b=nO(2)+1,nBas-nR(2)
jb = jb + 1
chi = 0d0
do kc=1,nS_sc
eps = Omega(kc)**2 + eta**2
chi = chi + rho(i,b,kc,2)*rho(a,j,kc,2)*Omega(kc)/eps
enddo
B_lr(nSa+ia,nSa+jb) = B_lr(nSa+ia,nSa+jb) - lambda*ERI_bbbb(i,j,b,a) + 2d0*lambda*chi
enddo
enddo
enddo
enddo
end if
!--------------------------------------------!
! Build BSE matrix for spin-flip transitions !
!--------------------------------------------!
if(ispin == 2) then
! abba block
ia = 0
do i=nC(1)+1,nO(1)
do a=nO(2)+1,nBas-nR(2)
ia = ia + 1
jb = 0
do j=nC(2)+1,nO(2)
do b=nO(1)+1,nBas-nR(1)
jb = jb + 1
chi = 0d0
do kc=1,nS_sc
eps = Omega(kc)**2 + eta**2
chi = chi + rho(i,b,kc,1)*rho(a,j,kc,2)*Omega(kc)/eps
enddo
B_lr(ia,nSa+jb) = B_lr(ia,nSa+jb) - lambda*ERI_aabb(i,j,b,a) + 2d0*lambda*chi
end do
end do
end do
end do
! baab block
ia = 0
do i=nC(2)+1,nO(2)
do a=nO(1)+1,nBas-nR(1)
ia = ia + 1
jb = 0
do j=nC(1)+1,nO(1)
do b=nO(2)+1,nBas-nR(2)
jb = jb + 1
chi = 0d0
do kc=1,nS_sc
eps = Omega(kc)**2 + eta**2
chi = chi + rho(i,b,kc,2)*rho(a,j,kc,1)*Omega(kc)/eps
enddo
B_lr(nSa+ia,jb) = B_lr(nSa+ia,jb) - lambda*ERI_aabb(j,i,a,b) + 2d0*lambda*chi
end do
end do
end do
end do
end if
end subroutine unrestricted_Bethe_Salpeter_B_matrix