Homogeneous and heterogeneous nucleation of Lennard-Jones liquids

TL;DR

This study investigates the nucleation processes in Lennard-Jones liquids using umbrella sampling, revealing how droplet structure, anisotropy, and impurity effects influence nucleation barriers and mechanisms across different conditions.

Contribution

It provides detailed insights into the free energy landscape, droplet structure, and impurity effects in Lennard-Jones nucleation, including spinodal behavior and lattice matching.

Findings

Nucleating droplets become more anisotropic at deep quenches.

Droplet structure shows randomly stacked hexagonal planes.

Free energy barrier minimized when impurity lattice matches crystalline phase.

Abstract

The homogeneous and heterogeneous nucleation of a Lennard-Jones liquid is investigated using the umbrella sampling method. The free energy cost of forming a nucleating droplet is determined as a function of the quench depth, and the saddle point nature of the droplets is verified using an intervention technique. The structure and symmetry of the nucleating droplets is found for a range of temperatures. We find that for deep quenches the nucleating droplets become more anisotropic and diffuse with no well defined core or surface. The environment of the nucleating droplets form randomly stacked hexagonal planes. This behavior is consistent with a spinodal nucleation interpretation. We also find that the free energy barrier for heterogeneous nucleation is a minimum when the lattice spacing of the impurity equals the lattice spacing of the equilibrium crystalline phase. If the lattice spacing of the impurity is different, the crystal grows into the bulk instead of wetting the impurity.