Calculate RMS displacement between two structures

        Args:
            struct1 (Structure): 1st structure
            struct2 (Structure): 2nd structure

        Returns:
            rms displacement normalized by (Vol / nsites) ** (1/3)
            and maximum distance between paired sites. If no matching
            lattice is found None is returned.

def get_rms_dist(self, struct1, struct2):
        """
        Calculate RMS displacement between two structures

        Args:
            struct1 (Structure): 1st structure
            struct2 (Structure): 2nd structure

        Returns:
            rms displacement normalized by (Vol / nsites) ** (1/3)
            and maximum distance between paired sites. If no matching
            lattice is found None is returned.
        """
        struct1, struct2 = self._process_species([struct1, struct2])
        struct1, struct2, fu, s1_supercell = self._preprocess(struct1, struct2)
        match = self._match(struct1, struct2, fu, s1_supercell, use_rms=True,
                            break_on_match=False)

        if match is None:
            return None
        else:
            return match[0], max(match[1])