Modeling Fluid Polyamorphism Through a Maximum-Valence Approach

TL;DR

This paper introduces a simple maximum-valence model to describe polyamorphism in single-component fluids, capturing liquid-gas and liquid-liquid transitions through different interaction types, with qualitative comparison to liquid sulfur.

Contribution

The paper presents a novel maximum-valence approach that models polyamorphism in fluids, incorporating multiple interaction types to explain complex phase behavior.

Findings

Model reproduces liquid-gas transition via van der Waals forces.

Inclusion of covalent bonds induces association phenomena.

Condition (iii) leads to liquid-liquid phase separation.

Abstract

We suggest a simple model to describe polyamorphism in single-component fluids using a maximum-valence approach. The model contains three types of interactions: i) atoms attract each other by van der Waals forces that generate a liquid-gas transition at low pressures, ii) atoms may form covalent bonds that induce association, and iii) bonded atoms attract or repel each other stronger than non-bonded atoms, thus generating liquid-liquid separation. As an example, we qualitatively compare this model with the behavior of liquid sulfur and show that condition (iii) generates a liquid-liquid phase transition in addition to the liquid-gas phase transition.