Three-body contribution to the adsorption potential of atoms on graphite

Calculations are presented of the three-body, triple-dipole (DDD) potential energy V(3)(r) of a noble-gas atom on a graphite surface. V(3)(r) is constructed from a sum over pairs of anisotropic C atoms at Ri and Rj of the DDD interaction u3(r,Ri,Rj). The result for V(3) is positive near the equilibrium position and of order 20% of the empirical well depth D. This term tends to reduce the corrugation of the equipotential surfaces. When incorporated in some model potentials (for He and Ne), the effect of the new term is qualitatively consistent with experimental data.