Binding mean spherical approximation for pairing ions: An exponential approximation and thermodynamics

The thermodynamics of mean spherical approximation for an arbitrary mixture of charged hard spheres with sticky-point attraction in the Wertheim formalism is derived for the most general case. It is shown that the electrostatic excess thermodynamics can be still computed from relatively simple formulas which depend on the screening parameter Gamma(B). We introduce also a new exponential approximation, which unlike the simpler mean spherical-like approximation discussed in our previous work, has the correct low density behavior. The restricted case of a binary mixture with a single association constant is discussed explicitly (C) 1996 American Institute of Physics.