The Study of the Molecular Diffusion in Gases and Liquids

Abstract

The molecular dynamics calculations of the velocity autocorrelation functions and the diffusion coefficients for argon and krypton atoms in argon have been carried out. The data of the molecular dynamics simulations are analyzed to understand the change of the diffusion mechanism with transition from dense gas to liquid. In dense gases, the diffusion mechanism is the same as in rarefied gases, and the temperature dependences of the diffusion coefficient are alike. A new diffusion mechanism appears in liquids. This diffusion mechanism isn’t connected with the jumping motion of the molecules. Probably, it is connected with the motion of the molecules group surrounding a molecule. Then the velocity of the molecule is relaxed with the decreasing of the average velocity of the molecules group. Various structures of the systems within the vapor – liquid phase transition region have been found and investigated. A comparison of the simulation results with the experimental data on diffusion in gaseous and liquid argon yields good agreement.