Many-body dispersion forces of polarizable clusters and liquids

Abstract

A system of atoms with embedded Drude dispersion oscillators interacting through dipole–dipole forces is simulated. Using path integrals it is shown that after the coordinates of the dispersion oscillators are integrated out, the atoms interact through many-body dispersion forces to all orders of the dipole–dipole interaction. Simulations are carried out on clusters to see if the presence of many-body forces leads to ground state geometries different from those predicted from two-body potentials. In addition, the polarizability tensor of clusters is determined as a function of cluster size. Simulations are also carried out for fluids to see how many-body forces affect the pair correlation function. Lastly, the long-range interaction between van der Waals clusters is compared with the predictions of a summation over site–site two-body interactions. It is found that many-body forces have only a minor effect on the low energy geometries of van der Waals clusters, a somewhat surprising result given that many-body forces do give an important contribution to surface free energies of clusters and liquids. The vibrational frequencies of the breathing mode decrease by approximately 10%.