INTEGRAL-EQUATION THEORY FOR CHARGED LIQUIDS - MODEL 2-2 ELECTROLYTES AND THE BRIDGE FUNCTION

The integral equation theory for a model 2-2 electrolyte is studied in detail. In this model electrolyte, the ions are assumed to be the same size, and interact via a continuous potential energy which behaves as the Coulomb potential at large distances and an inverse ninth power repulsion at short distances. The ions are embedded in a dielectric continuum of fixed dielectric constant, here taken to be 78.3 epsilon0 in order to model water at 25-degrees-C. The bridge function for this model is studied as a function of concentration (a) for six proposed closures, and (b) via "exact" inversion of data from computer simulations. A proposed closure derived from examination of the inverted bridge function yields predictions in good agreement with computer simulations. We emphasize the importance of choosing an "optimized" long-range potential, as opposed to the traditional Coulomb choice. A simple functional form for the bridge function results from this optimized choice of long-range potential.