A small-system ensemble Monte Carlo simulation of supersaturated vapor: Evaluation of barrier to nucleation

A small-system grand canonical ensemble Monte Carlo method is developed to evaluate cluster size distribution and barrier to the nucleation in a supersaturated Lennard-Jones vapor. The theoretical foundation is a physical cluster theory in which the Stillinger cluster is used as a prototypical physical cluster. Using method of Mayer’s cluster expansion, the cluster–vapor interaction is effectively taken into account. From a separate canonical ensemble Monte Carlo simulation using a test particle method, the averaged volume of the cluster is obtained and is also incorporated in the small-system ensemble simulation. By this implementation our simulation is computationally more efficient compared to that based on the n/v Stillinger cluster theory in that instead of searching the saddle point on a two-dimensional free energy surface a function of cluster size n and volume v) one needs only to find the peak on a free energy curve a function of n only . A comparison with the height of barrier obtained from a large-system ensemble Monte Carlo simulation K. Oh and X. C. Zeng, J. Chem. Phys. 110, 4471 1999 shows that omission of the vapor–cluster attraction can cause an overestimation of the height by several kBT . © 2000 American Institute of Physics. S0021-9606 00 50301-8