Investigation of the mass dependence of self-diffusion coefficients by molecular dynamics calculations: binary and ternary isotopic mixtures of atoms

Extensive molecular dynamics calculations have been used to study for the f irst time systematically the dependence of the self-diffusion coefficients D-i (i = 1,2, 3) in binary and ternary atomic isotopic mixtures on the part icle mass ratios m(2)* = m(2)/m(1) and m(3)* = m(3)/m(1) at different reduc ed temperatures T* and reduced particle number densities n*, using a Lennar d-Jones 12-6 potential and a hard-soft-spheres potential. In addition, the dependence of D-i values of binary mixtures on the mole fraction x(1) = 1 - x(2) was also investigated for some thermodynamic states. The calculated v alues of D-i can be represented quantitatively by exponential estimates of the form D-i = D-i(0)(m(2)*)(exi) in the case of binary mixtures and D-i = D-i(0)(m(2)*)(exi) (m(3)*)(exti) in the case of ternary mixtures. D-i(0) ar e the self-diffusion coefficients in reference mixtures of mass ratios m(2) * = m(3)* = 1. The dependence of the exponents ex(i)(m(2)*,T*,n*,x(1)) of b inary mixtures on m(2)*, T*, n*, and x(1) and the dependence of the exponen ts ext(i)(m(2)*, m(3)*, n*) of equimolar ternary mixtures at T* = 1.8 on th e exponents ex(i) of the constituent binary mixtures and on m(2)*, m(3)*, a nd n* are discussed.