The Early Crystal Nucleation Process in Hard Spheres shows Synchronised Ordering and Densification

TL;DR

This study uses computer simulations to reveal that in hard sphere fluids, crystallization begins with continuous ordering and densification, with collective particle movements occurring simultaneously, challenging traditional nucleation theories.

Contribution

It demonstrates that ordering and densification occur concurrently in early nucleation, with no separation of translational and orientational order, across different overcompression levels.

Findings

Hexagonal order appears before solid-like particles.

Density increases are synchronized with ordering.

No qualitative differences between medium and low overcompression.

Abstract

We investigate the early part of the crystal nucleation process in the hard sphere fluid using data produced by computer simulation. We find that hexagonal order manifests continuously in the overcompressed liquid, beginning approximately one diffusion time before the appearance of the first `solid-like' particle of the nucleating cluster, and that a collective influx of particles towards the nucleation site occurs simultaneously to the ordering process: the density increases leading to nucleation are generated by the same individual particle displacements as the increases in order. We rule out the presence of qualitative differences in the early nucleation process between medium and low overcompressions, and also provide evidence against any separation of translational and orientational order on the relevant lengthscales.