Heat capacity of square-well fluids of variable width

TL;DR

This study uses Monte Carlo simulations to measure the heat capacity of square-well fluids and compares the results with two theoretical models, revealing significant differences in predictive accuracy especially at varying temperatures and well widths.

Contribution

It provides the first detailed comparison of simulation data with perturbative and non-perturbative theories for heat capacity in square-well fluids across different conditions.

Findings

Barker-Henderson theory underestimates heat capacity at low to moderate temperatures.

Non-perturbative model agrees better with simulations, especially for small well widths.

Accuracy of the non-perturbative model decreases at high densities and low temperatures as well width increases.

Abstract

We have obtained by Monte Carlo NVT simulations the constant-volume excess heat capacity of square-well fluids for several temperatures, densities and potential widths. Heat capacity is a thermodynamic property much more sensitive to the accuracy of a theory than other thermodynamic quantities, such as the compressibility factor. This is illustrated by comparing the reported simulation data for the heat capacity with the theoretical predictions given by the Barker-Henderson perturbation theory as well as with those given by a non-perturbative theoretical model based on Baxter's solution of the Percus-Yevick integral equation for sticky hard spheres. Both theories give accurate predictions for the equation of state. By contrast, it is found that the Barker-Henderson theory strongly underestimates the excess heat capacity for low to moderate temperatures, whereas a much better agreement between theory and simulation is achieved with the non-perturbative theoretical model, particularly for small well widths, although the accuracy of the latter worsens for high densities and low temperatures, as the well width increases.