Even strong energy polydispersity does not affect the average structure and dynamics of simple liquids

TL;DR

This study shows that strong energy polydispersity in simple liquids does not significantly alter their average structure and dynamics, unlike size polydispersity, due to unchanged force distributions.

Contribution

It reveals that energy polydispersity preserves average structural and dynamic properties in simple liquids, contrasting with size polydispersity effects.

Findings

Average pair structure remains unchanged with energy polydispersity.

Dynamics are unaffected by strong energy polydispersity.

Force distributions are similar despite energy polydispersity.

Abstract

Size-polydisperse liquids have become standard models for avoiding crystallization, thereby enabling studies of supercooled liquids and glasses formed, e.g., by colloidal systems. Purely \textit{energy} polydisperse liquids have been studied much less, but provide an interesting alternative. We here study numerically the difference in structure and dynamics obtained by introducing these two kinds of polydispersity into systems of particles interacting via the Lennard-Jones and EXP pair potentials. To a very good approximation, the average pair structure and dynamics are unchanged even for strong energy polydispersity, while this is not the case for size-polydisperse systems. When the system at extreme energy polydispersity undergoes a continuous phase separation into lower and higher particle-energy regions whose structure and dynamics are different from the average, the average structure and dynamics are still virtually the same as for the monodisperse system. Our findings are consistent with the fact that the distribution of forces on the individual particles do not change when energy polydispersity is introduced, while they do change in the case of size polydispersity. A theoretical explanation of our findings remains to be found, however.