Calculation of self-diffusion coefficient and surface tension of liquid alkali metals using square-well fluid

Abstract

The self-diffusion coefficient (D) and the surface tension (γ) of the liquid alkali metals such as cesium (Cs) and rubidium (Rb) were calculated based on the Einstein's relation in a wide range of densities and temperatures. A developed mean spherical approximation (MSA) theory was applied to compute the direct correlation function using the effective square-well potential model for pair interaction in each temperature and density. The static structure factor, S(k), of the studied liquid species was evaluated by the proposed MSA theory in a wide range of wave vectors. The linear isothermal regularity equation of state was employed to determine the radial distribution function at a contact point at any thermodynamic state. A good agreement was obtained between the numerical results for both the D and γ values for the titled species and their available experimental data over the whole liquid range. For both liquids Cs and Rb, the temperature and density dependencies of the self-diffusion coefficient were investigated. Moreover, a correlation relation between the liquid surface tension and density and the temperature was found, in which the order of magnitude and sign of the coefficients were in good agreement with those obtained by experiment.