An extreme case of density scaling: The Weeks-Chandler-Andersen system at low temperatures

TL;DR

This study numerically investigates the Weeks-Chandler-Andersen system, revealing extreme density-scaling behavior and demonstrating strong invariance in structure and dynamics across wide temperature ranges, supported by a mean-field theory.

Contribution

It uncovers unprecedented variation in density-scaling exponent and develops a mean-field theory explaining the temperature dependence of virial potential-energy correlations.

Findings

Density-scaling exponent varies from below 5 to above 500.

Strong isomorph invariance observed over large temperature ranges.

Mean-field theory accurately fits low-temperature, low-density data.

Abstract

This paper studies numerically the Weeks-Chandler-Andersen (WCA) system, which is shown to obey hidden scale invariance with a density-scaling exponent that varies from below 5 to above 500. This unprecedented variation makes it advantageous to use the fourth-order Runge-Kutta algorithm for tracing out isomorphs. Good isomorph invariance of structure and dynamics is observed over more than three orders of magnitude temperature variation. For all state points studied, the virial potential-energy correlation coefficient and the density-scaling exponent are controlled mainly by the temperature. Based on the assumption of statistically independent pair interactions, a mean-field theory is developed that rationalizes this finding and provides an excellent fit to data at low temperatures and densities.