function sltcnd_2_kernel_ua_3b(nI, exc) result(hel)
integer, intent(in) :: nI(nel)
type(Excite_2_t), intent(in) :: exc
HElement_t(dp) :: hel
integer :: id(2, 2), ex(2, 2)
! Obtain spatial rather than spin indices if required
id = exc%val
ex = exc%val
hel = (0)
if (G1(ex(1, 1))%Ms == G1(ex(1, 2))%Ms) then
if (tReltvy .or. ((G1(ex(2, 1))%Ms == G1(ex(2, 2))%Ms) .and. &
(G1(ex(1, 1))%Ms == G1(ex(2, 2))%Ms))) then
hel = get_contact_umat_el_3b_sp(id(1, 1), id(1, 2), id(2, 1), id(2, 2)) - &
get_contact_umat_el_3b_sp(id(1, 1), id(1, 2), id(2, 2), id(2, 1))
end if
else
! We have an additional sign factor due to the exchange of the creation
! operators:
!a_(p-k)^+ a_(s+k)^+ a_q^+ a_q a_s a_p -> -a_q^+ a_(s+k)^+ a_(p-k)^+ a_q a_s a_p
!a_(p-k)^+ a_(s+k)^+ a_q^+ a_q a_s a_p -> -a_(p-k)^+ a_q^+ a_(s+k)^+ a_q a_s a_p
if (tReltvy .or. ((G1(ex(1, 1))%Ms == G1(ex(2, 1))%Ms) .and. &
(G1(ex(1, 2))%Ms == G1(ex(2, 2))%Ms))) then
hel = -get_contact_umat_el_3b_sap(id(1, 1), id(1, 2), id(2, 1), id(2, 2), nI)
end if
if (tReltvy .or. ((G1(ex(1, 1))%Ms == G1(ex(2, 2))%Ms) .and. &
(G1(ex(1, 2))%Ms == G1(Ex(2, 1))%Ms))) then
hel = hel + get_contact_umat_el_3b_sap(id(1, 1), id(1, 2), id(2, 2), id(2, 1), nI)
end if
end if
end function sltcnd_2_kernel_ua_3b