Ephemeral ice-like local environments in classical rigid models of liquid water

TL;DR

This study uses a data-driven SOAP approach to classify local environments in classical water models, revealing transient ice-like structures in liquid water at room temperature, aligning with recent ab initio findings.

Contribution

It introduces a SOAP-based method to compare classical water models and demonstrates the presence of ephemeral ice-like environments in liquid water.

Findings

Transient ice-like environments form in liquid water at room temperature.

Classical models can capture ephemeral local ice-like structures.

Results align with recent ab initio calculations.

Abstract

Despite great efforts over the past 50 years, the simulation of water still presents significant challenges and open questions. At room temperature and pressure, the collective molecular interactions and dynamics of water molecules may form local structural arrangements that are non-trivial to classify. Here we employ a data-driven approach built on Smooth Overlap of Atomic Position (SOAP) that allow us to compare and classify how widely used classical models represent liquid water. Macroscopically, the obtained results are rationalized based on water thermodynamic observables. Microscopically, we directly observed how transient ice-like ordered environments may dynamically/statistically form in liquid water, even above the freezing temperature, by comparing the SOAP spectra for different ice structures with those of the simulated liquid systems. This confirms recent ab initio-based calculations, but also reveals how the emergence of ephemeral local ice-like environments in liquid water at room conditions can be captured by classical water models.