Relabels all `Atoms` in numerical order.

        Parameters
        ----------
        start : int, optional
            Offset the labelling by `start` residues.

def relabel_atoms(self, start=1):
        """Relabels all `Atoms` in numerical order.

        Parameters
        ----------
        start : int, optional
            Offset the labelling by `start` residues.
        """
        counter = start
        for atom in self.get_atoms():
            atom.id = counter
            counter += 1
        return