Properties of liquid clusters in large-scale molecular dynamics nucleation simulations

R Angelil and J Diemand and KK Tanaka and H Tanaka, JOURNAL OF CHEMICAL PHYSICS, 140, 074303 (2014).

DOI: 10.1063/1.4865256

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. 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 +/- 0.05 and a/c = 0.5 +/- 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 thinner than planar equilibrium interfaces by 10%-30%. At the critical cluster size, the cluster central densities are between 5% and 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. (C) 2014 AIP Publishing LLC.

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