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quack/src/GW/BSE2_static_kernel_KA.f90

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2022-11-28 15:21:05 +01:00
subroutine BSE2_static_kernel_KA(eta,nBas,nC,nO,nV,nR,nS,lambda,eW,W,KA2_sta)
! Compute the second-order static BSE kernel for the resonant block (only for singlets!)
implicit none
include 'parameters.h'
! Input variables
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) :: lambda
double precision,intent(in) :: eW(nBas)
double precision,intent(in) :: W(nBas,nBas,nBas,nBas)
! Local variables
double precision :: dem,num
integer :: i,j,k,l
integer :: a,b,c,d
integer :: ia,jb
! Output variables
double precision,intent(out) :: KA2_sta(nS,nS)
!------------------------------------------------
! Compute BSE2 kernel
!------------------------------------------------
ia = 0
do i=nC+1,nO
do a=nO+1,nBas-nR
ia = ia + 1
jb = 0
do j=nC+1,nO
do b=nO+1,nBas-nR
jb = jb + 1
do k=nC+1,nO
do c=nO+1,nBas-nR
dem = - (eW(c) - eW(k))
num = 2d0*W(j,k,i,c)*W(a,c,b,k)
KA2_sta(ia,jb) = KA2_sta(ia,jb) - num*dem/(dem**2 + eta**2)
dem = + (eW(c) - eW(k))
num = 2d0*W(j,c,i,k)*W(a,k,b,c)
KA2_sta(ia,jb) = KA2_sta(ia,jb) + num*dem/(dem**2 + eta**2)
end do
end do
do c=nO+1,nBas-nR
do d=nO+1,nBas-nR
dem = - (eW(c) + eW(d))
num = 2d0*W(a,j,c,d)*W(c,d,i,b)
KA2_sta(ia,jb) = KA2_sta(ia,jb) + num*dem/(dem**2 + eta**2)
end do
end do
do k=nC+1,nO
do l=nC+1,nO
dem = - (eW(k) + eW(l))
num = 2d0*W(a,j,k,l)*W(k,l,i,b)
KA2_sta(ia,jb) = KA2_sta(ia,jb) - num*dem/(dem**2 + eta**2)
end do
end do
end do
end do
end do
end do
end subroutine BSE2_static_kernel_KA