Calculation of solvation properties using a combined expanded ensemble - Transition matrix Monte Carlo approach

A novel approach for calculating equilibrium solvation properties (free energies, entropies, etc.) was studied using molecular simulation. Two methods for calculating solvation properties at a given density or pressure were presented: one that provides these properties at a specific temperature and a second that enables one to obtain solvation properties over a range of temperatures. In both cases, an expanded ensemble was used to gradually increase the strength of interaction between a solute particle and the solvent through a series of subensembles. Solvation free energies at a specific temperature were calculated using transition probabilities from Monte Carlo moves to transfer the system to a neighboring subensemble. Transition probabilities in two dimensions, energy (or enthalpy in the constant pressure case) and subensemble, are necessary when calculating solvation free energies over a range of temperatures. Once transition probabilities were collected at a specified temperature, standard reweighting techniques were used to evaluate probabilities at different temperatures. These techniques were applied to the water-methane system as a means to examine the performance of the method. This is an abstract of a paper presented at the AIChE Annual Meeting and Fall Showcase (Cincinnati, OH 1/04/2005).