Get magnitude of difference between nonpolar and polar same branch
        polarization.

def get_polarization_change_norm(self, convert_to_muC_per_cm2=True, all_in_polar=True):
        """
        Get magnitude of difference between nonpolar and polar same branch
        polarization.
        """
        polar = self.structures[-1]
        a, b, c = polar.lattice.matrix
        a, b, c = a / np.linalg.norm(a), b / np.linalg.norm(
            b), c / np.linalg.norm(c)
        P = self.get_polarization_change(convert_to_muC_per_cm2=convert_to_muC_per_cm2,
                                         all_in_polar=all_in_polar).ravel()
        P_norm = np.linalg.norm(a * P[0] + b * P[1] + c * P[2])
        return P_norm