Thermodynamics of Asymmetric Primitive Model Electrolytes via the Hypernetted Chain Approximation.

The accuracy of the activity coefficient expression (Hansen-Vieillefosse-Belloni (HVB) equation), valid within the hypernetted-chain (HNC) approximation, was tested in a wide concentration range against newly obtained grand canonical Monte Carlo data for the size and charge asymmetric primitive model electrolytes. In some cases, uncharged hard sphere component was also present. The HVB expression enables a direct calculation of the excess chemical potential, without invoking the time consuming calculation via the Gibbs-Duhem relation. We found the Ornstein-Zernike (OZ)/HNC results for the mean activity coefficient, as well as for the reduced excess internal energy and osmotic coefficient, to be in good agreement with the machine calculations performed for the same model. The accuracy of the results was found to be dependent on the packing fraction of the solutions. The mean spherical approximation calculations were also used to describe the thermodynamics of these systems and compared with the OZ/HNC and simulation results.