Three-body interactions involving clusters and films

The three-body (triple dipole) interaction of Axilrod, Teller, and Muto (ATM) contributes 5-10% of the total energy of condensed phases of inert elements. It is shown in this paper for clusters and films that a much larger or smaller ATM contribution can arise for other geometries or other atomic species. The ratio R of the three-body interaction energy to the two-body energy is evaluated for a wide variety of configurations. This ratio varies considerably with the geometry. For highly polarizable atoms in certain geometries, the magnitude of the three-body energy is comparable to that of the two-body energy and can be either attractive or repulsive. Systematic trends are established and explained.