Mode-coupling analysis of the translational and rotational diffusion of polar liquids; acetonitrile and water

The translational and rotational motions of two representative polar liquids, water and acetonitrile, are investigated by the mode-coupling theory for molecular liquids based on the interaction-site model. The diffusive motion of acetonitrile agrees fairly well with that from the molecular-dynamics simulation. The pressure dependence of the translational and rotational diffusion coefficients is also in qualitative agreement with experiments. However, the reorientational relaxation of water is predicted to be much faster than that from experiments or simulations. The agreement between the theory and the simulation is partly improved by using the dynamic structure factor determined by the simulation. The effect of three-site correlation in the mode-coupling expression of the memory function is also examined. (C) 2003 Elsevier B.V. All rights reserved.