code: def get_rms_anonymous(self, struct1, struct2):
          
          struct1, struct2 = self._process_species([struct1, struct2])
          struct1, struct2, fu, s1_supercell = self._preprocess(struct1, struct2)
  
          matches = self._anonymous_match(struct1, struct2, fu, s1_supercell,
                                          use_rms=True, break_on_match=False)
          if matches:
              best = sorted(matches, key=lambda x: x[1][0])[0]
              return best[1][0], best[0]
          else:
              return None, None
docs: Performs an anonymous fitting, which allows distinct species in one
          structure to map to another. E.g., to compare if the Li2O and Na2O
          structures are similar.
  
          Args:
              struct1 (Structure): 1st structure
              struct2 (Structure): 2nd structure
  
          Returns:
              (min_rms, min_mapping)
              min_rms is the minimum rms distance, and min_mapping is the
              corresponding minimal species mapping that would map
              struct1 to struct2. (None, None) is returned if the minimax_rms
              exceeds the threshold.