In search of a precursor for crystal nucleation of hard and charged colloids

TL;DR

This study uses computer simulations and machine learning to investigate whether local structural fluctuations can predict crystal nucleation in hard and charged colloids, finding no evidence of precursors.

Contribution

It demonstrates that crystal nucleation in colloids occurs without detectable structural precursors, challenging previous hypotheses.

Findings

Crystallinity signs emerge simultaneously with nucleation.

No structural precursors detected before nucleation.

Machine learning methods reveal hidden structures in fluids.

Abstract

The interplay between crystal nucleation and the structure of the metastable fluid has been a topic of significant debate over recent years. In particular, it has been suggested that even in simple model systems such as hard or charged colloids, crystal nucleation might be foreshadowed by significant fluctuations in local structure around the location where the first nucleus arises. We investigate this using computer simulations of spontaneous nucleation events in both hard and charged colloidal particles. To detect local structural variations, we use both standard and unsupervised machine learning methods capable of finding hidden structures in the metastable fluid phase. We track numerous nucleation events for the face-centered cubic and body-centered cubic crystal on a local level, and demonstrate that all signs of crystallinity emerge simultaneously from the very start of the nucleation process. We thus conclude that there is no precursor for the nucleation of charged colloids.