(62h) Mesoscopic Canonical Ensemble

The Gibbs ensemble method of Panagiotopoulos opened up new avenues to molecular simulation studies of phase equilibrium in macroscopic systems, which comply with the thermodynamic limit principle. We have employed the ideas of the Gibbs ensemble method in our new technique named the mesoscopic canonical ensemble (MCE). MCE provides a rigorous framework for the description and molecular simulations of phase transformations in small systems that are beyond the thermodynamic limit, in particular, in fluids confined to nanoscale boundaries and traps. In MCE the sample system is considered in chemical equilibrium with a reference reservoir of finite volume called the gauge cell. The gauge cell volume determines the level of fluctuations in the sample system spanning the conditions of the canonical ensemble (zero gauge cell volume) and the grand canonical ensemble (infinite gauge cell volume). After a brief introduction into the statistical mechanics of MCE, we will present its application on two case study systems: condensation and cavitation of LJ fluid confined to (a) spherical cavities with rigid walls and (b) localized harmonic potential that bears characteristic features of Bose-Einstein condensation of cold gases in magnetic traps. Practical applications of MCE include among the others hydrogen storage in micropores of solid matrixes and gas separations relevant to clean energy technologies.