Generalized Rosenfeld-Tarazona scaling and high-density specific heat of simple liquids

TL;DR

This paper generalizes the Rosenfeld-Tarazona scaling for the excess heat capacity of simple liquids, showing that the exponent varies with material and density, and proposing an adjustable parameter for better data description.

Contribution

It introduces a generalized RT scaling with a density- and material-dependent exponent for the excess heat capacity of simple liquids.

Findings

The exponent in RT scaling varies across different fluids and conditions.

A generalized scaling form with an adjustable exponent better fits experimental data.

No universal exponent applies to all simple liquids, indicating material-specific behavior.

Abstract

The original Rosenfeld-Tarazona (RT) scaling of the excess energy in simple dense fluids predicts a $\propto T^{3/5}$ thermal correction to the fluid Madelung energy. This implies that the excess isochoric heat capacity scales as $C_{\rm v}^{\rm ex}\propto T^{-2/5}$. Careful examination performed in this paper demonstrates that the exponent $-2/5$ is not always optimal. For instance, in the Lennard-Jones fluid in some vicinity of the triple point, the exponent $-1/3$ turns out to be more appropriate. The analysis of the specific heat data in neon, argon, krypton, xenon, and liquid mercury reveals that no single value of the exponent exists, describing all the data simultaneously. Therefore we propose a generalized RT scaling in the form $C_{\rm v}^{\rm ex}\propto T^{-\alpha}$, where $\alpha$ is a density- and material-dependent adjustable parameter. The question concerning which material properties and parameters affect the exponent $\alpha$ and whether it can be predicted from general physical arguments requires further investigation.