Liquid Polymorphism and Density Anomaly in a Lattice Gas Model

TL;DR

This paper introduces a lattice gas model that links liquid polymorphism and density anomalies, revealing complex phase behavior driven by competing interactions.

Contribution

It presents a novel two-dimensional lattice gas model combining soft core potential and orientational variables to study liquid polymorphism and density anomalies.

Findings

Presence of two liquid phases in the phase diagram

Density anomaly associated with phase coexistence

Positive slope of the coexistence line between low and high density liquids

Abstract

We present a simple model for an associating liquid in which polymorphism and density anomaly are connected. Our model combines a two dimensional lattice gas with particles interacting through a soft core potential and orientational degrees of freedom represented through thermal \char`\"{}ice variables\char`\"{} . The competition between the directional attractive forces and the soft core potential leads to a phase diagram in which two liquid phases and a density anomaly are present. The coexistence line between the low density liquid and the high density liquid has a positive slope contradicting the surmise that the presence of a density anomaly implies that the high density liquid is more entropic than the low density liquid.