The EXP pair-potential system. II. Fluid phase isomorphs

TL;DR

This study examines the behavior of the EXP pair-potential system's fluid phase isomorphs, demonstrating that its structure and dynamics are largely invariant along these isomorphs, with methods for generating them compared.

Contribution

It introduces and compares methods for generating isomorphs in the EXP system's fluid phases, confirming invariance of structure and dynamics across a range of densities.

Findings

Reduced-unit structure and dynamics are isomorph invariant.

Approximate methods for generating isomorphs are effective.

Methods work well over a decade of density variation.

Abstract

This paper continues the investigation of the exponentially repulsive EXP pair-potential system of Paper I with a focus on isomorphs in the low-temperature gas and liquid phases. As expected from the EXP system's strong virial potential-energy correlations, the system's reduced-unit structure and dynamics are isomorph invariant to a good approximation. Three methods for generating isomorphs are compared: the small-step method that is exact in the limit of small density changes and two versions of the direct-isomorph-check method that allows for much larger density changes. Results from approximate methods are compared to those of the small-step method for each of three isomorphs generated by 230 one percent density increases, covering in all one decade of density variation. Both approximate methods work well.