code: def as_dict(self):
          
          d = {"@module": self.__class__.__module__,
               "@class": self.__class__.__name__,
               "charge": self._charge,
               "spin_multiplicity": self._spin_multiplicity,
               "sites": []}
          for site in self:
              site_dict = site.as_dict()
              del site_dict["@module"]
              del site_dict["@class"]
              d["sites"].append(site_dict)
          return d
docs: Json-serializable dict representation of Molecule