NONADDITIVE HARD-SPHERE REFERENCE SYSTEM FOR A PERTURBATIVE LIQUID-STATE THEORY OF BINARY-SYSTEMS

Up to now additive hard spheres have been used as reference systems in perturbation theories of binary liquid systems; this is due to the fact that only for this case are analytic expressions for the direct correlation functions available within the Percus-Yevick approximation. Here for the first time a Weeks-Chandler-Andersen perturbation theory for binary systems, using nonadditive hard spheres as a reference system for the repulsive parts of the potentials, is presented. The nonadditivity of realistic systems - as binary metal alloys - can therefore properly be taken into account. Treating nonadditive systems with additive reference systems by introducing additional (sometimes unphysical) parameters is no longer necessary, and our parameters - i.e., the three hard-sphere diameters - are determined uniquely. Including in a subsequent step the attractive forces by means of the optimized random phase approximation, it is found that agreement with other liquid state theories as well as with experimental scattering data is very good, even for extremely nonadditive systems. © 1990 American Institute of Physics.