  The motion of a multi-electronic atom in an external electro-magnetic field
is reconsidered. We prove that according to classical mechanics and
electrodynamics, the assumption that the interaction with the magnetic field is
described by means of a potential energy is no valid, and the trajectory of the
center of mass can be deflected by a magnetic field, even if the internal
angular momentum is zero. The characteristic equation of the corresponding
hamiltonian is not separable in three degrees of freedom for the hydrogen atom.
