Mixture-like behavior near a liquid-liquid phase transition in simulations of supercooled water

TL;DR

This study uses simulations of a water-like model to investigate a liquid-liquid phase transition, revealing mixture-like behavior near the critical point and providing estimates for its location.

Contribution

It demonstrates that supercooled water can be modeled as a two-component mixture near the liquid-liquid critical point, offering new insights into its phase behavior.

Findings

Mixture model accurately describes the liquid near the critical point.

Critical point location estimated from mixture fits.

Outside the anomaly region, the liquid is not well modeled as a mixture.

Abstract

In simulations of a water-like model (ST2) that exhibits a liquid-liquid phase transition, we test for the occurrence of a thermodynamic region in which the liquid can be modelled as a two-component mixture. We assign each molecule to one of two species based on the distance to its fifth-nearest neighbor, and evaluate the concentration of each species over a wide range of temperature and density. Our concentration data compare well with mixture-model predictions in a region between the liquid-liquid critical temperature and the temperature of maximum density. Fits of the model to the data in this region yield accurate estimates for the location of the critical point. We also show that the liquid outside the region of density anomalies is poorly modelled as a simple mixture.