Dispersion interactions in small zinc, cadmium, and mercury clusters.

Dispersion interactions in small clusters of group XII (Zn, Cd, Hg) metal atoms are studied at the CCSD(T) level with triple-ζ basis sets. A pair potential model together with a least-squares fit to the interaction potential energy surface is used to calculate interatomic dispersion coefficients, which are found to be in good agreement with atomistic calculations. The angular dependence of the dispersion interaction, extracted by explicitly accounting for the leading order electrostatic and induction terms, is determined with the aid of a coupled spherical harmonic expansion. The distance dependence of the orientation averaged dispersion energy is modeled by an integral average of our potential model, which is able to robustly account for the average dispersion energy to a remarkable degree.