Computer simulation of the nucleation and thermodynamics of microclusters

Abstract

Gas liquid equilibrium in finite systems is studied by computer simulation using molecular dynamics and Monte Carlo techniques. In overexpanded liquids, cavitation is observed. At some point in the expansion the system undergoes a transition from a liquid with cavities to a droplet in equilibrium with vapor. This transition is observed in the pV diagram of the system. A method is devised for counting the number of atoms in a cluster and thereby determining the cluster distribution function. The interface of a microcluster is compared to that of a planar sheet. The two are found to be very similar in density profile. In the course of this study homogeneous nucleation in a supersaturated gas is observed for the first time in a molecular dynamics study. Simple theories of nucleation in a finite system are considered. The free energy of formation of a droplet is found to have a maximum—a barrier to nucleation—and a minimum—stable equilibrium between a droplet and liquid. When gas imperfection is included, the barrier increases, and the stable cluster is destabilized.