Create a Molecule instance of the pymatgen library

        .. warning:: The `pymatgen library <http://pymatgen.org>`_ is imported
            locally in this function and will raise
            an ``ImportError`` exception, if it is not installed.

        Args:
            None

        Returns:
            :class:`pymatgen.core.structure.Molecule`:

def get_pymatgen_molecule(self):
        """Create a Molecule instance of the pymatgen library

        .. warning:: The `pymatgen library <http://pymatgen.org>`_ is imported
            locally in this function and will raise
            an ``ImportError`` exception, if it is not installed.

        Args:
            None

        Returns:
            :class:`pymatgen.core.structure.Molecule`:
        """
        from pymatgen import Molecule
        return Molecule(self['atom'].values,
                        self.loc[:, ['x', 'y', 'z']].values)