Potential energy of atoms near a metal surface.

The dependence of the atom-metal surface interaction potential on the response time of the metal electron gas is discussed. For an atom in its ground state, it is shown that the mirror-image potential of classical electrostatics can be retrieved if the metal response time in the Lifshitz formula is much shorter than the characteristic fluctuation time of the atom, whereas, for the opposite limit, the interaction potential of an atom in a spherically symmetric state is vanishingly small