Lattice-switch Monte Carlo for binary hard-sphere crystals

TL;DR

This paper extends the Lattice Switch Monte Carlo method to binary systems, enabling direct free energy calculations and phase diagram exploration for binary hard-sphere crystals, revealing stability of certain structures and insights into experimental observations.

Contribution

The authors develop a generalized Lattice Switch Monte Carlo method for binary systems, allowing efficient phase diagram computation and free energy evaluation in a single simulation.

Findings

AB2 and AB13 structures are confirmed as stable.

AB(CsCl) structure is not entropically stable at reported experimental conditions.

Method agrees with previous results at moderate size ratios.

Abstract

We show how to generalize the Lattice Switch Monte Carlo method to calculate the phase diagram of a binary system. A global coordinate transformation is combined with a modification of particle diameters, enabling the multi-component system in question to be explored and directly compared to a suitable reference state in a single Monte Carlo simulation. We use the method to evaluate the free energies of binary hard sphere crystals. Calculations at moderate size ratios, \alpha=0.58 and \alpha=0.73, are in agreement with previous results, and confirm AB2 and AB13 as stable structures. We also find that the AB(CsCl) structure is not entropically stable at the size ratio and volume at which it has been reported experimentally, and therefore that those observations cannot be explained by packing effects alone.