Solid-liquid coexistence of polydisperse fluids via simulation

TL;DR

This paper introduces a simulation method to accurately study the equilibrium freezing of polydisperse fluids, accounting for fixed polydispersity, and applies it to soft spheres to analyze solid-liquid coexistence.

Contribution

The authors generalize the phase switch Monte Carlo method to handle particle size polydispersity in simulations of fluid phase coexistence.

Findings

Small polydispersity affects the solid-liquid transition.

The method accurately predicts coexistence properties.

Results are relevant for soft sphere systems.

Abstract

We describe a simulation method for the accurate study of the equilibrium freezing properties of polydisperse fluids under the experimentally relevant condition of fixed polydispersity. The approach is based on the phase switch Monte Carlo method of Wilding and Bruce [Phys. Rev. Lett. {\bf 85}, 5138 (2000)]. This we have generalized to deal with particle size polydispersity by incorporating updates which alter the diameter $\sigma$ of a particle, under the control of a distribution of chemical potential differences $\tilde\mu(\sigma)$. Within the resulting isobaric semi-grand canonical ensemble, we detail how to adapt $\tilde\mu(\sigma)$ and the applied pressure such as to study coexistence, whilst ensuring that the ensemble averaged density distribution $\rho(\sigma)$ matches a fixed functional form. Results are presented for the effects of small degrees of polydispersity on the solid-liquid transition of soft spheres.