code: def get_rms_dist(self, struct1, struct2):
          
          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])
docs: 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.