Abstract
A new theoretical method is presented for predicting osmotic equilibria and activities, wherea bulk liquid and its corresponding vapor phase are simulated by means of molecular dynamicsusing explicit polarization. Calculated time-averaged number density profiles provide thevapor phase densities. The activity of the solvent and the corresponding osmotic coecient aredetermined by the vapor density at dierent solute concentrations with respect to the referencevapor density of the pure solvent. With the extended Debye-Huckel equation for the activitycoecient and the corresponding Gibbs-Duhem relation in addition the activity coecientsof the solutes are calculated by fitting the osmotic coecients. A simple model based on thecombination of Poisson processes and Maxwell-Boltzmann velocity distributions is introducedto interpret statistical phenomena observed during the simulations, which are related to evaporationand recondensation. This method is applied on various systems such as concentratedaqueous solutions of rare earth nitrates, mixtures of water and alcohols, and organic phases.The simulated activities, osmotic coecients, and activity coecients are in good agreementwith the experimental findings for the aqueous solutions of the rare earth nitrates.