def set_default_graph(self):
self.graph = MolecularGraph.from_geometry(self)<EOL>
Set self.graph to the default graph.

           This method is equivalent to::

              mol.graph = MolecularGraph.from_geometry(mol)

           with the default options, and only works if the graph object is not
           present yet.
           See :meth:`molmod.molecular_graphs.MolecularGraph.from_geometry`
           for more fine-grained control over the assignment of bonds.