Given a structure, returns back the structure scaled to predicted
        volume.
        Args:
            structure (Structure): structure w/unknown volume
            ref_structure (Structure): A reference structure with a similar
                structure but different species.
        Returns:
            a Structure object with predicted volume

def get_predicted_structure(self, structure, ref_structure):
        """
        Given a structure, returns back the structure scaled to predicted
        volume.
        Args:
            structure (Structure): structure w/unknown volume
            ref_structure (Structure): A reference structure with a similar
                structure but different species.
        Returns:
            a Structure object with predicted volume
        """
        new_structure = structure.copy()
        new_structure.scale_lattice(self.predict(structure, ref_structure))

        return new_structure