Structure, dynamics, and thermodynamics of benzene-Arn clusters (1⩽n⩽8 and n=19)

Abstract

We use a combination of molecular dynamics, Monte Carlo and geometry optimisation techniques to study benzene-Ar_n clusters for 1⩽n⩽19, with particular emphasis on BzAr₁₉. In particular, we discuss the difficulties which arise in the accurate simulation of heterogeneous clusters due to problems of ergodicity and nonadditive contributions to the energy. The sensitivity of minima, transition states and reaction pathways to parameters of the potential and the induction energy is also considered. An efficient integration scheme with adaptive step size due to Bulirsch and Stoer is employed in the molecular dynamics simulations. Both geometry optimisation and molecular dynamics are considered to evaluate the usefulness of the Jump–walking Monte Carlo method proposed by Frantz, Freeman, and Doll. This approach improves the ergodicity of canonical simulations using data from different temperatures which we achieved using multiple parallel runs. We then apply a multiple histogram method to calculate the relative number of states in phase space and various thermodynamic properties covering the full temperature range in the canonical and the microcanonical ensembles. The Monte Carlo and molecular dynamics simulations result in a consistent picture of transitions between minima and escape times. Finally, we consider the rate of side-crossing by Ar atoms in BzAr₁ and BzAr₁₉ and compare statistical theories with rates obtained from simulations.