docs: 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)