A molecular dynamics simulation of the diffusion of the solute (Au) and the self-diffusion of the solvent (Cu) in a very dilute liquid Cu-Au solution.

The identification of the manner in which a solute diffusion coefficient (D) might vary with temperature (T) in a fused metal or semimetal has led to considerable experimental study and some theoretical analysis. However, the conclusions of this work are inconsistent. In the present work, molecular dynamics studies of diffusion of a very dilute solute (Au) in liquid Cu are presented. Using the simple Enskog theory of diffusion, it is shown that the ratio of the diffusion constant of the solute to the diffusion constant of the solvent for a very dilute solution is approximately constant. This prediction is confirmed by molecular dynamics simulations although the values of ratios agree only within 20%-25%. In agreement with experiment, current simulations predict that within the usually investigated temperature range, the diffusion coefficient is linearly dependent on temperature. A very small contribution of parabolic behavior can only be observed for a temperature range much wider than that available for physical experiments due to materials limitations.