Evaluation of Osmotic Virial Coefficients via Restricted Gibbs Ensemble Simulations, with Support from Gas-Phase Mixture Coefficients

We present a method for computing osmotic virial coefficients in explicit solvent via simulation in a restricted Gibbs ensemble. Two equivalent phases are simulated at once, each in a separate box at constant volume and temperature and each in equilibrium with a solvent reservoir. For osmotic coefficient B-N, a total of N solutes are individually exchanged back and forth between the boxes, and the average distribution of solute numbers between the boxes provides the key information needed to compute B-N. Separately, expressions are developed for B-N as a series in solvent reservoir density rho(1), with the coefficients of the series expressed in terms of the usual gas-phase mixture coefficients B-ij. Normally, the B-ij are defined for an infinite volume, but we suggest that the observed dependence of B-ij on system size L can be used to estimate L dependence of the B-N, allowing them to be computed accurately at L -> infinity while simulating much smaller system sizes than otherwise possible. The methods for N = 2 and 3 are demonstrated for two- component mixtures of size-asymmetric additive hard spheres. The proposed methods are demonstrated to have greater precision than established techniques, for a given amount of computational effort. The rho(1) series for B-N when applied by itself is (for this noncondensing model) found to be the most efficient in computing accurate osmotic coefficients for the solvent densities considered here.

Automated summary

The method proposed in this paper allows for the computation of osmotic virial coefficients in explicit solvent through simulation in a restricted Gibbs ensemble. It demonstrates greater precision than established techniques and enables accurate computation at smaller system sizes.