Expects a DOS object and finds the gap

        Args:
            tol: tolerance in occupations for determining the gap
            abs_tol: Set to True for an absolute tolerance and False for a
                relative one.
            spin: Possible values are None - finds the gap in the summed
                densities, Up - finds the gap in the up spin channel,
                Down - finds the gap in the down spin channel.

        Returns:
            (gap, cbm, vbm):
                Tuple of floats in eV corresponding to the gap, cbm and vbm.

def get_interpolated_gap(self, tol=0.001, abs_tol=False, spin=None):
        """
        Expects a DOS object and finds the gap

        Args:
            tol: tolerance in occupations for determining the gap
            abs_tol: Set to True for an absolute tolerance and False for a
                relative one.
            spin: Possible values are None - finds the gap in the summed
                densities, Up - finds the gap in the up spin channel,
                Down - finds the gap in the down spin channel.

        Returns:
            (gap, cbm, vbm):
                Tuple of floats in eV corresponding to the gap, cbm and vbm.
        """

        tdos = self.y if len(self.ydim) == 1 else np.sum(self.y, axis=1)
        if not abs_tol:
            tol = tol * tdos.sum() / tdos.shape[0]
        energies = self.x
        below_fermi = [i for i in range(len(energies))
                       if energies[i] < self.efermi and tdos[i] > tol]
        above_fermi = [i for i in range(len(energies))
                       if energies[i] > self.efermi and tdos[i] > tol]
        vbm_start = max(below_fermi)
        cbm_start = min(above_fermi)
        if vbm_start == cbm_start:
            return 0.0, self.efermi, self.efermi
        else:
            # Interpolate between adjacent values
            terminal_dens = tdos[vbm_start:vbm_start + 2][::-1]
            terminal_energies = energies[vbm_start:vbm_start + 2][::-1]
            start = get_linear_interpolated_value(terminal_dens,
                                                  terminal_energies, tol)
            terminal_dens = tdos[cbm_start - 1:cbm_start + 1]
            terminal_energies = energies[cbm_start - 1:cbm_start + 1]
            end = get_linear_interpolated_value(terminal_dens,
                                                terminal_energies, tol)
            return end - start, end, start