Homogeneous bubble nucleation in water at negative pressure: A Voronoi polyhedra analysis

TL;DR

This study uses Voronoi analysis and MFPT methods to investigate homogeneous vapor bubble nucleation in metastable water under negative pressure, revealing differences in nucleation behavior above and below the spinodal line.

Contribution

It introduces a Voronoi-based approach combined with MFPT to analyze bubble nucleation in water, providing new insights into nucleation rates and critical cluster sizes.

Findings

MFPT curves match classical expectations above the spinodal

Nucleation rate from MFPT is about 8 orders of magnitude higher than classical theory

Below the spinodal, MFPT shows a monotonic behavior indicating different instability

Abstract

We investigate vapor bubble nucleation in metastable TIP4P/2005 water at negative pressure via the Mean First Passage Time (MFPT) method using the volume of the largest bubble as a local order parameter. We identify the bubbles in the system by means of a Voronoi-based analysis of the Molecular Dynamics trajectories. By comparing the features of the tessellation of liquid water at ambient conditions to those of the same system with an empty cavity we are able to discriminate vapor (or interfacial) molecules from the bulk ones. This information is used to follow the time evolution of the largest bubble until the system cavitates at 280 K above and below the spinodal line. At the pressure above the spinodal line, the MFPT curve shows the expected shape for a moderately metastable liquid from which we estimate the bubble nucleation rate and the size of the critical cluster. The nucleation rate estimated using Classical Nucleation Theory turns out to be about 8 order of magnitude lower than the one we compute by means of MFPT. The behavior at the pressure below the spinodal line, where the liquid is thermodynamically unstable, is remarkably different, the MFPT curve being a monotonous function without any inflection point.