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

Thomas E Gartner,Pablo G Debenedetti,Roberto Car,Salvatore Torquato

doi:10.1038/s41467-021-23639-2

Thomas E Gartner, Pablo G Debenedetti + Show 2 more

Open Access

https://doi.org/10.1038/s41467-021-23639-2

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Journal: Nature Communications	Publication Date: Jun 7, 2021
Citations: 16	License type: open-access

Affiliation: Princeton University

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.

Highlights

Much attention has been devoted to water’s metastable phase behavior, including polyamorphism, and the hypothesized liquid-liquid transition and associated critical point
Computational studies of water-like models have demonstrated that water may undergo a first-order liquid–liquid transition (LLT) into high-density and low-density liquids (HDL and LDL, respectively);[13] the resulting line of liquid–liquid coexistence terminates in a metastable liquid–liquid critical point (LLCP)[14]
LLTs have been experimentally observed in some pure substances and a growing body of evidence supports the existence of an LLCP in supercooled liquid water at positive pressures[21,22,23]

Summary

Introduction

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. 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. We 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. Computational studies of water-like models have demonstrated that water may undergo a first-order liquid–liquid transition (LLT) into high-density and low-density liquids (HDL and LDL, respectively);[13] the resulting line of liquid–liquid coexistence terminates in a metastable liquid–liquid critical point (LLCP)[14]. Simulations of several classes of water models of varying accuracy and complexity have yielded evidence consistent with an LLT24–27

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