Molecular Theory of Nucleating Clusters in Tenuous Atmospheres
The nucleation of droplets and crystallites from supercooled or supersaturated vapors near a triple point is studied from both a phenomenological and a microscopic point of view. From the phenomenological discussion we conclude that the proximity to the triple point, the degree of supersaturation, and whether one phase wets the interface between the other two phases at the triple point in question, are essential ingredients in understanding the variety of nucleation mechanisms which are encountered near a triple point. The microscopic perspective is advanced by the construction of a cluster-integral series developed to calculate the droplet and crystallite partition functions involved in the classical theory of nucleation. The cluster -integral expansion coefficients are evaluated for droplets of argon and argon-krypton mixtures by an efficient inversely -restricted sampling Monte-Carlo algorithm. The series is used to construct the free energy surface for droplet growth in supersaturated vapors, and to predict the condensation curve for a wide range of temperatures. The inversely -restricted sampling algorithm can be modified in order to calculate the partition function of bulk systems. Another technique is proposed, designed especially for water, for the calculation of the bulk free energy. The harmonic potential of a glassy structure found from a quench of the liquid is used as a reference in an umbrella-sampling Monte-Carlo calculation. The harmonic free energy of the glass is calculated by molecular dynamics.
- Pub Date:
- STATISTICAL MECHANICS;
- Physics: Molecular