Thermal conductivity of fluids with steeply repulsive potentials

We consider the thermal conductivity of steeply repulsive inverse power flu ids (SRP) in which the particles interact with a pair potential, phi (r) = epsilon(sigma /r)". The time correlation function for the heat flux, C-lamb da(t), and the time average, C-lambda(0) are calculated numerically by mole cular dynamics simulations, and accurate expressions for these are also der ived for the SRP fluid. We show, by molecular dynamics simulations, that cl ose to the hard-sphere limit this time correlation function has the same an alytic form as for the shear and pressure correlation functions for the she ar and bulk viscosity, i.e. C-lambda(t)/C-lambda(0) = 1 T* (nt*)(2) + O((nt *) (4)), where T* = k(B)T/epsilon, is the reduced temperature, k(B) is Bolt zmann's constant and t* =(epsilon /m sigma (2))(1/2)t is the reduced time. The thermal conductivity for the limiting case of hard spheres is numerical ly very close to that given by the traditional Enskog relation. At low dens ities the normalized relaxation times are typically largest for the thermal conductivity, followed by shear and then bulk viscosity. Close to the maxi mum fluid density, the latter two increase rapidly with density (especially for the shear) but continue a monotonic decline for the thermal conductivi ty. This reflects the relative insensitivity of the thermal conductivity to the approach to the fluid-solid phase boundary.