(335e) Evaluation Of Aqueous Partial Molar Volumes From Molecular Simulations

Sangwai, A. V., Tulane University
Ashbaugh, H., Tulane University

The direct evaluation of infinite dilution partial molar volumes in aqueous solution is challenging because the partial molar volume is determined as the difference between two large isothermal/isobaric simulation volumes with and without the solute. Kirkwood-Buff (KB) theory provides an alternate route to evaluation of the partial molar volume, however, the required correlation function integrals are notoriously long-ranged and oscillatory. We show that by introducing an auxiliary site screening length, the KB correlation integrals become short-ranged, converging within the first hydration shell of the solute. By subsequently dividing the integral on a local solute proximity basis, we are able to accurately evaluate the partial molar volumes of molecularly complex, heterogeneous solutes. The proximal correlation functions of chemically related groups (e.g., methylene groups or ether oxygens) are found to be essentially identical, irrespective of the identity of the parent solute. This naturally suggests a group contribution method for the partial molar volume based on solute-water intermolecular correlations.