Transport properties of expanded rubidium: potential dependence

Abstract

The effect of the potential shape on the transport properties of rubidium (Rb) metal along the liquid–vapor co-existence curve has been studied at six thermodynamic states by assuming that the particles of the system are interacting via the Lennard–Jones (LJ) potential with same effective size of the particle and well depth of the potential as that of the corresponding liquid–metal (LM) potential. Self-diffusion coefficient and coefficient of shear viscosity of expanded Rb have been calculated by using a simple model, which employs sum rules and provides a good description of transport coefficients both for LMs and LJ fluids. We have found that the sum rules are able to account for the observed differences in the behavior of velocity auto-correlation functions (VACFs) of LM and LJ fluids. The fact that the back scattering effects are more pronounced in LMs than in the case of LJ fluids can be understood in terms of enhanced values of frequency sum rules in case of harder potential. It is found that the normalized stress auto-correlation function decays much faster in harder potential than in liquid metal. The effect of the potential shape on the self-diffusion and the shear viscosity is found to decrease as one moves toward the critical point from near the triple point. The contribution due to three particle correlations is found to be more important in case of metals than in LJ fluids.