Vacancy-stabilized crystalline order in hard cubes

TL;DR

This study reveals that vacancies in hard cube systems stabilize a crystalline phase and enhance positional order, with vacancies being delocalized and present at significant concentrations near phase coexistence.

Contribution

It demonstrates that vacancies can stabilize and increase order in hard cube crystals, a novel insight into defect roles in colloidal systems.

Findings

Vacancies reach ~6.4% near coexistence.

Vacancies increase positional order.

Vacancies are delocalized and hard to detect.

Abstract

We examine the effect of vacancies on the phase behavior and structure of systems consisting of hard cubes using event-driven molecular dynamics and Monte Carlo simulations. We find a first-order phase transition between a fluid and a simple cubic crystal phase that is stabilized by a surprisingly large number of vacancies, reaching a net vacancy concentration of ~6.4% near bulk coexistence. Remarkably, we find that vacancies increase the positional order in the system. Finally, we show that the vacancies are delocalized and therefore hard to detect.