CONSISTENCY CONDITIONS FOR THE INTEGRAL-EQUATIONS OF LIQUID STRUCTURES

A thermodynamic consistency principle is established for the closure r elations in integral equations that can yield accurate correlation fun ctions as well as accurate thermodynamic properties. A brief tour d'ho rizon is given for existing consistency approaches. In addition to the common pressure consistency and the pressure-energy consistency, we i ntroduce a third requirement based on the Gibbs-Duhem relation. We fou nd that Gibbs-Duhem relation, mediated through the chemical potential, is instrumental in procuring accurate behavior of the bridge function and cavity function in the overlapping region (0 < r < sigma). We tes t the Lennard-Jones fluid over wide ranges of T and rho* (T* as low a s 0.72 and rho up to 0.90). For more than 15 state points we obtain e xcellent agreement in internal energy, pressure, and chemical potentia l. Comparison with Monte Carlo data on the bridge function and the rad ial distribution function also shows that the present approach is high ly accurate.