Two-dimensional core-softened model with water like properties. Study by thermodynamic perturbation theory

Urbic Urbic

doi:10.5488/cmp.16.43605

Abstract

Thermodynamic properties of the particles interacting through smooth version of Stell-Hemmer interaction were studied using Wertheim's thermodynamic perturbation theory. The temperature dependence of molar volume, heat capacity, isothermal compressibility and thermal expansion coefficient at constant pressure for different number of bonding sites on particle were evaluated. The model showed water-like anomalies for all evaluated quantities, but thermodynamic perturbation theory does not properly predict the dependence of these properties at a fixed number of bonding points.

Highlights

They were Stell and Hemmer who first proposed core-softened potentials in 1970 [1]
They reported the existence of the low-density liquid phase and the high-density liquid phase obtained for 3D model using molecular dynamics (MD) simulations
We find out that the thermodynamic perturbation theory (TPT) does not properly capture the results for simulations as well as it does not predict the maxima in density or minima in molar volume

Summary

Introduction

They were Stell and Hemmer who first proposed core-softened potentials in 1970 [1]. In their early work, they stressed that negative curvature in interaction potential might lead to a second critical point in addition to a standard liquid-gas critical point. Franseze et al [13] suggested that the liquid-liquid phase transition and its critical point might be caused by the potential with two characteristic distances (hard core and soft core). Scala et al [16] carried out MD simulations of 2D discrete and smoothed version of potential to study liquid anomalies These studies were continued by Buldyrev et al [17] to explore liquid-liquid phase transition for 2D and 3D version of potentials and by Almudallal et al [18]. They both produced phase diagrams for a discrete version of potential with liquid anomalies, and no liquid-liquid critical point in stable liquid region was obtained. Í Ö Figure 1. (Color online) The core-softened potentialμ (solid line) with both contributions (LJ — long dashed line and Gaussian part — dashed line)

Monte Carlo simulation details

Thermodynamic perturbation theory

Results

Conclusion