Imaginary time Gaussian dynamics of the Ar_3 cluster

TL;DR

This paper introduces a computationally efficient frozen Gaussian method for simulating the thermodynamics of atomic clusters, successfully capturing quantum effects and phase transitions in the argon trimer.

Contribution

A new frozen Gaussian approximation for imaginary time propagators that is less computationally demanding and effective for cluster dynamics.

Findings

Identified a classical-like dissociation transition at ~20 K in Ar_3.

Quantum effects cause deviations in energy and heat capacity at low temperatures.

Artificial confinement significantly impacts thermodynamic properties.

Abstract

Semiclassical Gaussian approximations to the Boltzmann operator have become an important tool for the investigation of thermodynamic properties of clusters of atoms at low temperatures. Usually, numerically expensive thawed Gaussian variants are applied. In this article, we introduce a numerically much cheaper frozen Gaussian approximation to the imaginary time propagator with a width matrix especially suited for the dynamics of clusters. The quality of the results is comparable to that of thawed Gaussian methods based on the single-particle ansatz. We apply the method to the argon trimer and investigate the dissociation process of the cluster. The results clearly show a classical-like transition from a bounded moiety to three free particles at a temperature T ~ 20 K, whereas previous studies of the system were not able to resolve this transition. Quantum effects, i.e., differences with the purely classical case manifest themselves in the low-temperature behavior of the mean energy and specific heat as well as in a slight shift of the transition temperature. We also discuss the influence of an artificial confinement of the atoms usually introduced to converge numerical computations. The results show that restrictive confinements often implemented in studies of clusters can influence the thermodynamic properties drastically. This finding may have implications on other studies of atomic clusters.