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.
Highlights
We investigate the early part of the crystal nucleation process in the hard sphere fluid using data produced by computer simulation
As a typical first-order phase transition, crystallization from the metastable melt begins with a nucleation process
A hard sphere model is the starting point for many theoretical treatments of granular, fluid, glassy, and crystalline systems and may be sufficient without further refinement if excluded volume interactions are more significant than long-range forces
Summary
As a typical first-order phase transition, crystallization from the metastable melt begins with a nucleation process. A computational study by Russo and Tanaka has examined structure and density changes for a set of nucleating trajectories at a number density φσ3 ≈ 1.02, where σ is the diameter of a particle Augmenting these trajectories with fluctuation data drawn from the metastable liquid, they note a coupling of order and density, but state that “the density increase is foreshadowed by the prestructuring of the nucleus,” adopting a position which we will crudely summarise as “order-first.”. We test the expectation based on work by Kawasaki and Tanaka, Tan et al., Barros and Klein, and Schilling et al. that weakly ordered precursors to crystallization should or might be present, and find that hexagonal ordering manifests gradually and continuously in the fluid prior to the formation of the first definitively solid-like particles, without evidence of any intermediate state We show that local and mediumrange density changes take place simultaneously to the initial formation of (weak) translational and orientational order, presenting an order-with-density model which is distinct from the order-first mechanism preferred by Russo and Tanaka. We test the expectation based on work by Kawasaki and Tanaka, Tan et al., Barros and Klein, and Schilling et al. that weakly ordered precursors to crystallization should or might be present, and find that hexagonal ordering manifests gradually and continuously in the fluid prior to the formation of the first definitively solid-like particles, without evidence of any intermediate state
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