First Density Correction to the Transport Coefficients for a Square Well Gas: Temperature Dependence and Bound State Effects

The temperature dependence of transport properties of a moderately dense square well gas is studied in order to understand the effects of attractive forces (particularly bound states). The quantum cluster expansions of the Green -Kubo time correlation functions for the thermal conductivity, shear viscosity, and self-diffusion coefficients are given, and exact expressions to zeroth (Boltzmann level) and first order in the density are obtained. Specializing to Boltzmann statistics and the classical square well potential allows calculations of the kinetic potential parts of the first density correction; the important contributions to the remaining triple collision parts are discussed. Good agreement with molecular dynamics results is found; quantitative difference from real fluids are observed, however. Possible reasons for the discrepancies are discussed. A brief description of the ultility and limitations of the hard sphere model is given for comparison. The dynamics structure factor is calculated for a dense fluid of hard spheres and compared with recent neutron scattering data for Krypton.