Effect of three-body forces on the statics and dynamics of SF6–(Rg)n and (Rg)13 clusters

Abstract

Molecular dynamics and Monte Carlo simulations are used to examine the effect on the structural properties of heterogeneous SF6–(Ar)n and SF6–(Kr)n clusters, and on the melting behavior of heterogeneous SF6–(Ar)n and homogeneous (Ar)13 and (Kr)13 clusters, of including the three-body Axilrod–Teller–Muto triple–dipole dispersion energies in the total potential energy surface governing the dynamics of the system. The behavior of these systems is governed by potentials constructed from the best available two-body interactions, and from accurate constrained dipole oscillator strength values for the triple–dipole dispersion energy coefficients reported here for the first time. The structural studies show that (virtually) all isomers are destablized by inclusion of the three-body terms, with the ‘‘stacked’’ or ‘‘nonwetting’’ structures being destablized relatively more than isomeric ‘‘monolayer’’ or ‘‘wetting’’ structures. However, the qualitative trends in relative stability are unchanged; in particular, the preference for the SF6 to be fully solvated in larger clusters formed with Ar, but to lie on the surface of larger clusters formed with Kr, remains unchanged. In contrast, the melting temperatures of the stacked and monolayer isomers of the heterogeneous SF6–(Ar)12 cluster undergo substantial change on inclusion of the three-body terms, the former dropping from ca. 30 to 22 K and the latter from 10 to 6 K. The melting temperatures of the homogeneous (Ar)13 and (Kr)13 icosahedral isomers also decreased on inclusion of the three-body interactions, and the resulting values are quite different than those obtained using the commonly accepted ‘‘effective’’ two-body LJ(12,6) pair potentials for these systems.