Stokes-Einstein Relation in Pure Alkali Metals and their Alloys

Abstract

Stokes-Einstein relation is a convenient way to evaluate diffusion properties in liquids from viscosity results (and vice-versa). However, the accuracy of this relation in the case of atomic fluids is often debated as it was initially established in the case of a big Brownian particle immersed in a fluid. Especially, the question is raised to properly define the hydrodynamic radius entering the formula, as well as the constant depending on the boundary conditions at the surface of the particle. In this study, we use our results of viscosity and self-diffusion coefficient obtained by molecular dynamics simulations in the case of alkali metals and their alloys to evaluate the applicability of Stokes-Einstein relation in the case of these liquids. In the case of pure metals, its validity is discussed over a wide range of thermodynamic states, from ambient pressure up to several gigapascals. In the case of alloys, the evolution of its accuracy as a function of temperature and composition is considered. Both definitions of hydrodynamic radius and boundary conditions constant are examined.