List of types of specie. Only works for ordered structures.
        Disordered structures will raise TypeError.

def types_of_specie(self):
        """
        List of types of specie. Only works for ordered structures.
        Disordered structures will raise TypeError.
        """
        if not self.is_ordered:
            raise TypeError("""\
types_of_species cannot be used with disordered structures and partial occupancies.
Use OrderDisorderedStructureTransformation or EnumerateStructureTransformation
to build an appropriate supercell from partial occupancies.""")

        # Cannot use set since we want a deterministic algorithm.
        types = []
        for site in self:
            if site.specie not in types:
                types.append(site.specie)
        return types