Relabels all Atoms in numerical order, offset by the start parameter.

        Parameters
        ----------
        start : int, optional
            Defines an offset for the labelling.

def relabel_atoms(self, start=1):
        """Relabels all Atoms in numerical order, offset by the start parameter.

        Parameters
        ----------
        start : int, optional
            Defines an offset for the labelling.
        """
        counter = start
        for atom in self.get_atoms(ligands=True):
            atom.id = counter
            counter += 1
        return