Microcanonical ensemble simulation method applied to discrete potential fluids

TL;DR

This paper extends the microcanonical ensemble simulation method to simple fluids, enabling efficient calculation of thermodynamic properties across a range of temperatures in a single run, demonstrated on square-well fluids.

Contribution

The authors develop a novel algorithm that applies microcanonical ensemble simulations to discrete-potential fluids, allowing continuous temperature coverage and high-accuracy thermodynamic measurements.

Findings

Accurate internal energies and heat capacities for square-well fluids.

The new method covers a continuous temperature range in one simulation.

Enhanced applicability of the H"uller-Pleimling method to discrete potentials.

Abstract

In this work we extend the applicability of the microcanonical ensemble simulation method, originally proposed to study the Ising model (A. H\"uller and M. Pleimling, Int. Journal of Modern Physics C, 13, 947 (2002), arxiv:cond-mat/0110090), to the case of simple fluids. An algorithm is developed by measuring the transition rates probabilities between macroscopic states, that has as advantage with respect to conventional Monte Carlo NVT (MC-NVT) simulations that a continuous range of temperatures are covered in a single run. For a given density, this new algorithm provides the inverse temperature, that can be parametrized as a function of the internal energy, and the isochoric heat capacity is then evaluated through a numerical derivative. As an illustrative example we consider a fluid composed of particles interacting via a square-well (SW) pair potential of variable range. Equilibrium internal energies and isochoric heat capacities are obtained with very high accuracy compared with data obtained from MC-NVT simulations. These results are important in the context of the application of H\"uller-Pleimling method to discrete-potential systems, that are based on a generalization of the SW and Square-Shoulder fluids properties.