(733c) Evaluation of Osmotic Virial Coefficients with Support from Gas Phase Mixture Coefficients

The osmotic virial formalism expresses the osmotic pressure of a solution as a power series in solute density. It derives inspiration from the virial equation of state, but the key difference being the interactions between solutes are mediated by a potential of mean force. The osmotic virials are rich with physical meaning, and they can facilitate modeling and understanding of fluid behavior in many ways. A large number of interactions (which increase with the order of coefficient) exist between solute and solvent, which pose a significant challenge in accurately and precisely computing the osmotic virial coefficients. In this paper, we present a restricted Gibbs ensemble approach where we simulate two boxes that are in a thermodynamic but not physical contact. We employ the rejection-free geometric cluster algorithm to enhance sampling, and we examine the performance of the method for different solute-solvent systems and concentrations. To correct for the finite-size effects, we augment our results with previously known and easy-to-compute gas-phase mixture virial coefficients. We also use gas-phase mixture virials in a standalone fashion to obtain osmotic virial coefficients. The proposed methods are demonstrated for two-component mixtures of size-asymmetric additive hard spheres. The results thus obtained using the proposed methods have greater precision than those available in the literature for a given amount of computational effort. We also observe that gas-phase mixture virial coefficients standalone provide the best estimate for the second and third osmotic virial coefficient for the non-condensing model studied.