Relaxation of Collective Excitations in LJ-13 Cluster

TL;DR

This study uses molecular dynamics simulations to analyze how collective excitations in an argon 13-atom cluster behave and dampen with temperature, revealing a critical temperature where collective stability sharply declines.

Contribution

It introduces a detailed analysis of the temperature-dependent damping of collective excitations in LJ-13 clusters, highlighting a characteristic temperature affecting stability.

Findings

Sharp change in damping behavior at ~7 K

Below this temperature, collective excitations are stable

Above this temperature, single particle excitations dominate

Abstract

We have performed classical molecular dynamics simulation of $Ar_{13}$ cluster to study the behavior of collective excitations. In the solid ``phase'' of the cluster, the collective oscillation of the monopole mode can be well fitted to a damped harmonic oscillator. The parameters of the equivalent damped harmonic oscillator-- the damping coefficient, spring constant, time period of oscillation and the mass of the oscillator -- all show a sharp change in behavior at a kinetic temperature of about $7.0^oK$. This marks yet another characteristic temperature of the system, a temperature $T_s$ below which collective excitations are very stable, and at higher temperatures the single particle excitations cause the damping of the collective oscillations. We argue that so long as the cluster remains confined within the global potential energy minimum the collective excitations do not decay; and once the cluster comes out of this well, the local potential energy minima pockets act as single particle excitation channels in destroying the collective motion. The effect is manifest in almost all the physical observables of the cluster.