A Monte Carlo method for chemical potential determination in single and multiple occupancy crystals

TL;DR

This paper introduces a Monte Carlo method for accurately measuring the chemical potential and free energy of single and multiple occupancy crystalline solids within a single simulation, revealing complex phase behavior.

Contribution

It presents a novel Monte Carlo scheme that efficiently determines chemical potentials and free energies for cluster crystals, including multiple occupancy phases, in a unified framework.

Findings

Method successfully measures chemical potential in single and cluster crystals.

Application reveals an infinite cascade of critical points in cluster phases.

Provides precise statistical uncertainties for thermodynamic quantities.

Abstract

We describe a Monte Carlo scheme which, in a single simulation, yields a measurement of the chemical potential of a crystalline solid. Within the isobaric ensemble, this immediately provides an estimate of the system free energy, with statistical uncertainties that are determined precisely and transparently. An extension to multiple occupancy ("cluster") solids permits the direct determination of the cluster chemical potential and hence the equilibrium conditions. We apply the method to a model exhibiting cluster crystalline phases, where we find evidence for an infinite cascade of critical points terminating coexistence between crystals of differing site occupancies.