Two methods were compared for the calculation of Maxwell-Stefan diffusion coefficients. The first method was a non-equilibrium molecular dynamics algorithm, in which the system was driven away from equilibrium and the system response was monitored. The second method was the equilibrium molecular dynamics calculation of the appropriate Green-Kubo equation. Simulations were performed for systems of 250 and 300 Lennard-Jones particles at various densities and temperatures. The systems were divided into two or three components by attaching a colour label to the particles. Since a colour label played no role in the dynamics, the Maxwell-Stefan diffusion coefficients of the binary and ternary systems were equal to the self-diffusion coefficient. In dense fluids, the system response to an external perturbation was not a first-order process, and the diffusion coefficients could not be determined from the short term response in the non-equilibrium molecular dynamics method. Only the long term response could be used, after a steady state was reached. In binary systems the Maxwell-Stefan diffusion coefficients, determined by the Green-Kubo method, were more accurate than the non-equilibrium molecular dynamics coefficients. Since in the non-equilibrium molecular dynamics method only the long term response could be used, the Green-Kubo method was also less time consuming and was therefore preferred for the calculation of the Maxwell-Stefan diffusion coefficients. In ternary systems the Green Kubo method was tested for the 250 particle system. The Maxwell-Stefan diffusion coefficients agreed well with the self-diffusion coefficient. For low mole fractions of the coloured components the diffusion coefficients were less accurate.

Using Molecular Dynamics to Obtain Maxwell-Stefan Diffusion Coefficients in Liquid Systems. Van De Ven-Lucassen, I.M.J.J., Vlugt, T.J.H., Van Der Zanden, A.J.J., Kerkhof, P.J.A.M.: Molecular Physics, 1998, 94[3], 495-503