Homogeneous and heterogeneous nucleation of Lennard-Jones liquids

摘要

The homogeneous and heterogeneous nucleation of a Lennard-Jones liquid isinvestigated using the umbrella sampling method. The free energy cost offorming a nucleating droplet is determined as a function of the quench depth,and the saddle point nature of the droplets is verified using an interventiontechnique. The structure and symmetry of the nucleating droplets is found for arange of temperatures. We find that for deep quenches the nucleating dropletsbecome more anisotropic and diffuse with no well defined core or surface. Theenvironment of the nucleating droplets form randomly stacked hexagonal planes.This behavior is consistent with a spinodal nucleation interpretation. We alsofind that the free energy barrier for heterogeneous nucleation is a minimumwhen the lattice spacing of the impurity equals the lattice spacing of theequilibrium crystalline phase. If the lattice spacing of the impurity isdifferent, the crystal grows into the bulk instead of wetting the impurity.