get_helement_k_space_hub_ex_mat Function

    function get_helement_k_space_hub_ex_mat(nI, ic, ex, tpar) result(hel)
        integer, intent(in) :: nI(nel), ic, ex(2, ic)
        logical, intent(in) :: tpar
        HElement_t(dp) :: hel

        !todo: if 2-body-transcorrelation, we can have triple excitations now..
        ! fix that here.. (and also in a lot of other parts in the code..)

        if (ic == 0) then
            ! the diagonal is just the sum of the occupied one-particle
            ! basis states
            hel = get_diag_helement_k_sp_hub(nI)

        else if (ic == 2) then

            hel = get_offdiag_helement_k_sp_hub(nI, ex, tpar)

        else if (ic == 3 .and. t_trans_corr_2body) then

            hel = get_3_body_helement_ks_hub(ex, tpar)

        else

            hel = h_cast(0.0_dp)

        end if

    end function get_helement_k_space_hub_ex_mat