Further details on the phase diagram of hard ellipsoids of revolution

TL;DR

This study uses replica exchange Monte Carlo simulations to explore the phase diagram of hard ellipsoids, revealing a rich sequence of phases and transitions, including isotropic fluid, plastic solid, stretched-fcc, and sm2 structures, with some transitions being high order.

Contribution

It introduces a novel simulation approach starting from sm2 crystal structures to better understand phase behavior of ellipsoids with various anisotropies.

Findings

Identification of multiple phases including sm2 and stretched-fcc structures.

Observation of first-order and high-order phase transitions.

Confirmation of sm2 structure's role in maximizing packing density.

Abstract

In recent work we revisited the phase diagram of hard ellipsoids of revolution (spheroids) by means of replica exchange Monte Carlo simulations. This was done by setting random initial configurations, and allows to confirm the formation of sm2 crystal structures at high densities [Phys. Rev. E 75, 020402 (2007)] for large anisotropies and stretched-fcc for small anisotropies. In this work we employed the same technique but setting the starting cells as sm2 crystal structures having the maximum known packing density [Phys. Rev. Lett. 92, 255506 (2004)]. This procedure yields a very rich behavior for quasi-spherical oblates and prolates. These systems, from low to high pressures, show the following phases: isotropic fluid, plastic solid, stretched-fcc solid, and sm2 solid. The first three transitions are first order, whereas the last one is a subtle, probably high order transition. This picture is consistent with the fact of having the sm2 structure capable of producing the maximally achievable density.