Local order and crystallization of dense polydisperse hard spheres

TL;DR

This study uses advanced simulation techniques to explore local order and crystallization in dense polydisperse hard spheres, revealing density-dependent geometric order growth and a unique crystal structure formation.

Contribution

It demonstrates the application of swap Monte Carlo to equilibrate dense polydisperse spheres and uncovers novel insights into local order and crystallization patterns.

Findings

Local geometric order grows at high density

Crystallization involves a unique aluminum diboride structure

Correlation lengths of icosahedral arrangements are quantified

Abstract

Computer simulations give precious insight into the microscopic behavior of supercooled liquids and glasses, but their typical time scales are orders of magnitude shorter than the experimentally relevant ones. We recently closed this gap for a class of models of size polydisperse fluids, which we successfully equilibrate beyond laboratory time scales by means of the swap Monte Carlo algorithm. In this contribution, we study the interplay between compositional and geometric local orders in a model of polydisperse hard spheres equilibrated with this algorithm. Local compositional order has a weak state dependence, while local geometric order associated to icosahedral arrangements grows more markedly but only at very high density. We quantify the correlation lengths and the degree of sphericity associated to icosahedral structures and compare these results to those for the Wahnstr\"om Lennard-Jones mixture. Finally, we analyze the structure of very dense samples that partially crystallized following a pattern incompatible with conventional fractionation scenarios. The crystal structure has the symmetry of aluminum diboride and involves a subset of small and large particles with size ratio approximately equal to 0.5.