Entropy-scaling laws for diffusion coefficients in liquid metals under high pressures

Abstract

Molecular dynamic simulations on the liquid copper and tungsten are used to investigate the empirical entropy-scaling laws D*=A exp(BSex), proposed independently by Rosenfeld and Dzugutov for diffusion coefficient, under high pressure conditions. We show that the scaling laws hold rather well for them under high pressure conditions. Furthermore, both the original diffusion coefficients and the reduced diffusion coefficients exhibit an Arrhenius relationship DM=DM0 exp(−EM/KBT), (M=un,R,D) and the activation energy EM increases with increasing pressure, the diffusion pre-exponential factors (DR0 and DD0) are nearly independent of the pressure and element. The pair correlation entropy, S2, depends linearly on the reciprocal temperature S2=−ES/T, and the activation energy, ES, increases with increasing pressure. In particular, the ratios of the activation energies (Eun, ER, and ED) obtained from diffusion coefficients to the activation energy, ES, obtained from the entropy keep constants in the whole pressure range. Therefore, the entropy-scaling laws for the diffusion coefficients and the Arrhenius law are linked via the temperature dependence of entropy.