Voids in liquids: peculiarities of molecular dynamics simulation of fluid systems

TL;DR

This paper explores the origins of large voids observed in molecular dynamics simulations of liquids, clarifying their relation to temperature and phase regions.

Contribution

It identifies conditions under which large cavities appear in simulations, linking them to temperature and phase behavior, and illustrates these with examples.

Findings

Large voids occur above the critical temperature.

Void formation is linked to two-phase liquid-gas regions.

Simulations show cavities consistent with phase transition conditions.

Abstract

Molecular dynamics is a powerful tool to investigate the properties of fluid systems. However, a correct interpretation of the results of simulations is required. In particular, some simulations show appearance of large voids in liquids, which contradicts our common sense on what is liquid. In the present paper we discuss the origin of large cavities liquids in molecular dynamics simulations. We demonstrate that the cavities appear either if the temperature of the system is above the critical temperature of liquid-gas transition or if the system is in two-phase liquid-gas region. These conclusions are illustrated by several examples from literature and our own simulations.