Abstract: Molecular dynamics simulation has been carried out to study the self-diffusion in pure supercritical fluid and Maxwell-Stefan mutual diffusion in binary supercritical Ar-Kr solution. In the supercritical fluid, the temperature dependence of the self-diffusion coefficient obeys the Arrhenius relation quite well, and the calculated activation energy decreases with increasing density. In the binary supercritical Ar-Kr solution, the concentration dependences of both self-diffusion and Maxwell-Stefan mutual diffusion coefficients are obtained. The self-diffusion coefficients of Ar and Kr increase with increasing molar fraction of Ar. The calculated Maxwell-Stefan diffusion coefficients are larger than those predicted by the Darken relation. The results also show that the velocity cross correlation is not negligible and positive, this system can not be treated as an ideal system which is different from Ar-Kr solution in the normal state where the Darken relation is applicable.

Key words: Supercritical fluid, Mixture, Diffusivity, Molecular dynamics simulation