Penetrable-Square-Well fluids: Analytical study and Monte Carlo simulations

TL;DR

This paper develops an approximate analytical theory for penetrable square-well fluids, validated by Monte Carlo simulations, exploring their structural, thermodynamic properties, and phase behavior, including the Fisher-Widom line.

Contribution

It introduces a novel approximate theory for penetrable square-well fluids applicable at any density and low penetrability, extending previous low-density analytical results.

Findings

The theory accurately predicts structural and thermodynamic properties in the low-penetrable regime.

Monte Carlo simulations confirm the validity range of the theoretical approach.

The study identifies the influence of penetrability on the Fisher-Widom line and fluid-fluid transition.

Abstract

We study structural and thermophysical properties of a one-dimensional classical fluid made of penetrable spheres interacting via an attractive square-well potential. Penetrability of the spheres is enforced by reducing from infinite to finite the repulsive energy barrier in the pair potentials As a consequence, an exact analytical solution is lacking even in one dimension. Building upon previous exact analytical work in the low-density limit [Santos \textit{et al.}, Phys. Rev. E \text{77}, 051206 (2008)], we propose an approximate theory valid at any density and in the low-penetrable regime. By comparison with specialized Monte Carlo simulations and integral equation theories, we assess the regime of validity of the theory. We investigate the degree of inconsistency among the various routes to thermodynamics and explore the possibility of a fluid-fluid transition. Finally we locate the dependence of the Fisher-Widom line on the degree of penetrability. Our results constitute the first systematic study of penetrable spheres with attractions as a prototype model for soft systems.