Density minimum and liquid-liquid phase transition

TL;DR

This study uses high-resolution simulations to explore the phase behavior of ST2 water, revealing the density minimum and its connection to liquid anomalies and the liquid-liquid critical point in a tetrahedral network model.

Contribution

It precisely locates the liquid-liquid critical point in ST2 water and clarifies the origin of the density minimum related to tetrahedral network formation.

Findings

Identified the density minimum in the liquid state.

Mapped the relationship between anomalies and the LLCP.

Linked the density minimum to the approach of a defect-free tetrahedral network.

Abstract

We present a high-resolution computer simulation study of the equation of state of ST2 water, evaluating the liquid-state properties at 2718 state points, and precisely locating the liquid-liquid critical point (LLCP) occurring in this model. We are thereby able to reveal the interconnected set of density anomalies, spinodal instabilities and response function extrema that occur in the vicinity of a LLCP for the case of a realistic, off-lattice model of a liquid with local tetrahedral order. In particular, we unambiguously identify a density minimum in the liquid state, define its relationship to other anomalies, and show that it arises due to the approach of the liquid structure to a defect-free random tetrahedral network of hydrogen bonds.