Returns:
            dict with element symbol and reduced amount e.g.,
            {"Fe": 2.0, "O":3.0}.

def to_reduced_dict(self):
        """
        Returns:
            dict with element symbol and reduced amount e.g.,
            {"Fe": 2.0, "O":3.0}.
        """
        d = self.composition.to_reduced_dict
        d['charge'] = self.charge
        return d