Predictions of Dynamic Behavior Under Pressure for Two Scenarios to Explain Water Anomalies

TL;DR

This study uses simulations and calculations to analyze water's dynamic behavior under pressure, revealing a crossover in molecular motion and differences between two theoretical scenarios, aiding in understanding water's anomalies.

Contribution

It demonstrates that pressure effects on water's dynamics differ significantly between the liquid-liquid critical point and singularity free scenarios, providing a way to distinguish them.

Findings

Dynamic crossover from non-Arrhenius to Arrhenius behavior in water.

Pressure impacts dynamics differently in the two scenarios.

Crossover linked to hydrogen bond fluctuations and heat capacity.

Abstract

Using Monte Carlo simulations and mean field calculations for a cell model of water we find a dynamic crossover in the orientational correlation time $\tau$ from non-Arrhenius behavior at high temperatures to Arrhenius behavior at low temperatures. This dynamic crossover is independent of whether water at very low temperature is charaterized by a ``liquid-liquid critical point'' or by the ``singularity free'' scenario. We relate $\tau$ to fluctuations of hydrogen bond network and show that the crossover found for $\tau$ for both scenarios is a consequence of the sharp change in the average number of hydrogen bonds at the temperature of the specific heat maximum. We find that the effect of pressure on the dynamics is strikingly different in the two scenarios, offering a means to distinguish between them.