sltcnd_0_tc_ua Function

    pure function sltcnd_0_tc_ua(nI, exc) result(hel)
        integer, intent(in) :: nI(nel)
        type(Excite_0_t), intent(in) :: exc
        HElement_t(dp) :: hel
        integer :: i, j, k

        ! get the diagonal matrix element up to 2nd order
        hel = sltcnd_0_base_ua(nI, exc)
        ! then add the 3-body part
        do i = 1, nel - 2
            do j = i + 1, nel - 1
                do k = j + 1, nel
                    hel = hel + get_lmat_el_ua(nI(i), nI(j), nI(k), nI(i), nI(j), nI(k))
                end do
            end do
        end do

    end function sltcnd_0_tc_ua