Effect of Energy Polydispersity on the Nature of Lennard-Jones Liquids

TL;DR

This study investigates how energy polydispersity affects Lennard-Jones liquids, demonstrating they remain Roskilde-simple and retain isomorphs, despite particle segregation and reduced correlation at higher polydispersity levels.

Contribution

It extends previous work by showing energy polydispersity preserves the Roskilde-simple nature and isomorph invariance in Lennard-Jones liquids, with insights into segregation effects.

Findings

Energy polydisperse LJ liquids are Roskilde-simple.

Particle segregation increases with polydispersity, reducing virial-potential energy correlation.

Isomorphs remain a good approximation despite energy polydispersity.

Abstract

In the companion paper [T. S. Ingebrigtsen and H. Tanaka, J. Phys. Chem. B 119, 11052 (2015)] the effect of size polydispersity on the nature of Lennard-Jones (LJ) liquids, which represent most molecular liquids without hydrogen bonds, was studied. More specifically, it was shown that even highly size polydisperse LJ liquids are Roskilde-simple (RS) liquids. RS liquids are liquids with strong correlation between constant volume equilibrium fluctuations of virial and potential energy and are simpler than other types of liquids. Moreover, it was shown that size polydisperse LJ liquids have isomorphs to a good approximation. Isomorphs are curves in the phase diagram of RS liquids along which structure, dynamics, and some thermodynamic quantities are invariant in dimensionless (reduced) units. In this paper, we study the effect of energy polydispersity on the nature of LJ liquids. We show that energy polydisperse LJ liquids are RS liquids. However, a tendency of particle segregation which increases with the degree of polydispersity leads to a loss of strong virial-potential energy correlation, but is mitigated with increasing temperature and/or density. Isomorphs are a good approximation also for energy polydisperse LJ liquids, although particle-resolved quantities display a somewhat poorer scaling compared to the mean quantities along the isomorph.