Molecular dynamics simulation of self-diffusion and Maxwell-Stefan diffusion coefficients in liquid mixtures of methanol and water

Self-diffusion coefficients and Maxwell-Stefan diffusion coefficients in li quids have been determined by the equilibrium molecular dynamics calculatio n of the appropriate Green-Kubo equation. Simulations of water, methanol an d mixtures of water and methanol have been carried out to calculate the dif fusion coefficients at 300 K. Tn order to study the influence of the force field on the calculated self-diffusion coefficients of the pure liquids, tw o different force fields for each component have been used. The Van Leeuwen /Smit force field calculated the self-diffusion of methanol accurately. The SPC/E force field gave the best, but moderate, results for water. In mixtu res of water and methanol the self-diffusion coefficients of:both component s were-more accurate at high mole fractions of methanol. This can be explai ned by the better performance of the methanol force field. The Maxwell-Stef an diffusion coefficients in the mixtures of methanol and water agreed fair ly well with the experimental values. More accurate results can be obtained by using optimised parameters in the water force field, and by enlarging t he integration time and the duration of the simulation runs.