Squared sum of total displacements for these atoms.

        Args:
            None

        Returns:
            (Float): The square of the summed total displacements for these atoms.

def collective_dr_squared( self ):
        """
        Squared sum of total displacements for these atoms.

        Args:
            None

        Returns:
            (Float): The square of the summed total displacements for these atoms.
        """
        return sum( np.square( sum( [ atom.dr for atom in self.atoms ] ) ) )