A mode-coupling approach to the attractive interaction effect on the solute diffusion in liquids

The effect of the solute-solvent and the solvent-solvent attractive interac tions on the diffusion coefficient of the solute is studied by the mode-cou pling theory. The mode-coupling part of the friction coefficient in our cal culation is compared with that of molecular dynamics simulation. The theory qualitatively reproduces the increase in the friction coefficient with the solute-solvent attractive interaction, although the absolute value is larg er than the simulation. A theoretical scheme is further provided to divide the memory function into attractive and repulsive components, and a mode-co upling approximation is introduced to both components separately. It is fou nd that the solute-solvent interaction affects the attractive friction main ly, in agreement with the simulation. Further analyses reveal the presence of the large cross term of the attractive and repulsive random forces. When the solvent-solvent attractive interaction is weakened while keeping the s olute-solvent interaction fixed, the mode-coupling friction is increased, w hich is opposite to the simulation results. (C) 2001 American Institute of Physics.