Free energies of molecular clusters determined by guided mechanical disassembly

TL;DR

This paper introduces a method to compute the excess free energy of molecular clusters by mechanically disassembling them in simulations, using guide particles and the Jarzynski equality, simplifying previous approaches.

Contribution

The study presents a novel simulation technique for directly extracting cluster free energies without comparing multiple cluster sizes, applicable to complex systems.

Findings

Consistent free energy results with previous studies.

Method applicable to clusters of 5 to 27 atoms.

Advantages and limitations of the disassembly scheme discussed.

Abstract

The excess free energy of a molecular cluster is a key quantity in models of the nucleation of droplets from a metastable vapour phase; it is often viewed as the free energy arising from the presence of an interface between the two phases. We show how this quantity can be extracted from simulations of the mechanical disassembly of a cluster using guide particles in molecular dynamics. We disassemble clusters ranging in size from 5 to 27 argon-like Lennard-Jones atoms, thermalised at 60 K, and obtain excess free energies, by means of the Jarzynski equality, that are consistent with previous studies. We only simulate the cluster of interest, in contrast to approaches that require a series of comparisons to be made between clusters differing in size by one molecule. We discuss the advantages and disadvantages of the scheme and how it might be applied to more complex systems.