Properties of Liquid Clusters in Large-scale Molecular Dynamics Nucleation Simulations

Abstract

We have performed large-scale Lennard-Jones molecular dynamics simulations of homogeneous vapor-to-liquid nucleation, with $10^9$ atoms. This large number allows us to resolve extremely low nucleation rates, and also provides excellent statistics for cluster properties over a wide range of cluster sizes. The nucleation rates, cluster growth rates, and size distributions are presented in Diemand et al. [J. Chem. Phys. {\bf 139}, 74309 (2013)], while this paper analyses the properties of the clusters. We explore the cluster temperatures, density profiles, potential energies and shapes. A thorough understanding of the properties of the clusters is crucial to the formulation of nucleation models. Significant latent heat is retained by stable clusters, by as much as $\Delta kT=0.1\epsilon$ for clusters with size $i=100$. We find that the clusters deviate remarkably from spherical - with ellipsoidal axis ratios for critical cluster sizes typically within $b/c=0.7\pm 0.05$ and $a/c=0.5\pm 0.05$. We examine cluster spin angular momentum, and find that it plays a negligible role in the cluster dynamics. The interfaces of large, stable clusters are thiner than planar equilibrium interfaces by $10-30\%$. At the critical cluster size, the cluster central densities are between $5-30\%$ lower than the bulk liquid expectations. These lower densities imply larger-than-expected surface areas, which increase the energy cost to form a surface, which lowers nucleation rates.

16 pages, 19 figures, accepted for publication in J. Chem. Phys

References in corpus (1)

• Systematic Improvement of Classical Nucleation Theory

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