Vapor Phase Homogeneous Nucleation and the Thermodynamic Properties of Small Clusters of Argon Atoms

The steady state rate of homogeneous nucleation in a vapor of Lennard-Jones spheres has been calculated using statistical mechanical techniques to compute the equilibrium concentrations of clusters in the vapor. All degrees of freedom of the clusters are explicitly considered. The harmonic approximation is used in the calculation of vibrational contributions to the cluster partition functions and the rigid body approximation is used in the calculation of rotational contributions. The Gibbs free energy of cluster formation as a function of cluster size is calculated and its dependence on temperature is examined. Size effects on the vibrational free energy are found to be mainly energetic rather than entropic. The rate of nucleation as a function of pressure is calculated at four temperatures and found to have a behavior similar to what would be expected from “liquid drop” model calculations.