# Crystalline clusters in mW water: stability, growth, and grain boundaries

## TL;DR

This study uses numerical simulations to analyze the stability, growth, and grain boundaries of crystalline clusters in mW water, revealing size-dependent stability and the influence of grain boundaries on polymorph selection.

## Contribution

It introduces a detailed analysis of size-dependent stability and grain boundary effects in crystalline water clusters, highlighting mechanisms behind polymorph competition.

## Key findings

- Small clusters favor Ice 0 phase stability.
- Large clusters favor Ice I phase stability.
- Grain boundaries hinder growth of metastable phases.

## Abstract

With numerical simulations of the mW model of water, we investigate the energetic stability of crystalline clusters for both Ice I (cubic and hexagonal ice) and for the metastable Ice 0 phase as a function of the cluster size. Under a large variety of forming conditions, we find that the most stable cluster changes as a function of size: at small sizes the Ice 0 phase produces the most stable clusters, while at large sizes there is a crossover to Ice I clusters. We further investigate the growth of crystalline clusters with the seeding technique and study the growth patterns of different crystalline clusters. While energetically stable at small sizes, the growth of metastable phases (cubic and Ice 0) is hindered by the formation of coherent grain boundaries. A five-fold symmetric twin boundary for cubic ice, and a newly discovered coherent grain boundary in Ice 0, that promotes cross nucleation of cubic ice. Our work reveals that different local structures can compete with the stable phase in mW water, and that the low energy cost of particular grain boundaries might play an important role in polymorph selection.