Charged hard dumbbell in the binding mean-spherical approximation

A simple model for charged hard dumbbell is proposed in the binding mean-sp herical approximation (BIMSA). The thermodynamic properties are analytical solutions of the unique screening parameter Gamma (B) with full association . Critical point and vapour-liquid coexistence curve are identical to those of Kalyuzhnyi, Yu. V., 1998, Molec. Phys., 94, 735, where a site-site inte gral equation has to be solved. Substituting Gamma without association for Gamma (B), the BIMSA reduces to the simple interpolation scheme (SIS). A si mple interpolation between the SIS and the BIMSA is proposed: this gives th e critical point. (T*(c) = 0.0525, rho*(c) = 0.0640) which, for the time be ing, is the closest to the computer simulation results. Similarity between the charged hard dumbbell and the restricted primitive model of electrolyte is also addressed.