Manifestations of metastable criticality in the long-range structure of model water glasses

TL;DR

This study uses molecular dynamics simulations to reveal how the liquid-liquid critical point influences the long-range structure of water glasses, linking metastable phase behavior with non-equilibrium properties.

Contribution

It demonstrates the structural signature of the liquid-liquid critical point in water glasses and compares it with systems lacking such a critical point, providing new insights into water's phase behavior.

Findings

Pronounced increase in long-range density fluctuations near the critical pressure.

Absence of these signatures in non-critical model systems.

Pressure-dependent non-equilibrium index in water-like systems.

Abstract

Much attention has been devoted to water's metastable phase behavior, including polyamorphism (multiple amorphous solid phases), and the hypothesized liquid-liquid transition and associated critical point. However, the possible relationship between these phenomena remains incompletely understood. Using molecular dynamics simulations of the realistic TIP4P/2005 model, we found a striking signature of the liquid-liquid critical point in the structure of water glasses, manifested as a pronounced increase in long-range density fluctuations at pressures proximate to the critical pressure. By contrast, these signatures were absent in glasses of two model systems that lack a critical point. We also characterized the departure from equilibrium upon vitrification via the non-equilibrium index; water-like systems exhibited a strong pressure dependence in this metric, whereas simple liquids did not. These results reflect a surprising relationship between the metastable equilibrium phenomenon of liquid-liquid criticality and the non-equilibrium structure of glassy water, with implications for our understanding of water phase behavior and glass physics. Our calculations suggest a possible experimental route to probing the existence of the liquid-liquid transition in water and other fluids.