setup_tmat_k_space Subroutine

    subroutine setup_tmat_k_space(in_lat)
        ! routine which sets up the (diagonal) t-matrix in the k-space
        ! the dimensionality and connectivity of nearest and next-nearest
        ! neighbors influences that!
        class(lattice), intent(in), optional :: in_lat
        character(*), parameter :: this_routine = "setup_tmat_k_space"

        if (present(in_lat)) then
            if (all(nBasisMax == 0)) then
                call setup_nbasismax(in_lat)
            end if

            if (.not. associated(G1)) then
                call setup_g1(in_lat)
            end if
            ! else assume it is already setup correctly

            if (.not. associated(tmat2d)) then
                ! call the already implemented hubbard tmat calculator..
                ! for now only.. in the future we should do this standalone
                call CALCTMATHUB(in_lat%get_nsites() * 2, nBasisMax, bhub, &
                                 ttilt, G1,.not. in_lat%is_k_space(), in_lat%is_periodic())

            end if

        else
            call Stop_All(this_routine, "not yet implemented!")
        end if

    end subroutine setup_tmat_k_space