Water-methanol mixtures with non-Lorentz-Berthelot combining rules: A feasibility study

To examine a possibility to predict qualitatively correctly the properties of water-alcohol mixtures using pure fluid non-polarizable interaction potential models, a family of non-Lorentz-Berthelot combing rules was used in simulations on the water-methanol mixtures defined by the standard TIP4P (water) and OPLS (methanol) interaction models. A certain strategy to locate the region of the cross parameters yielding, potentially, a minimum in the partial molar volume of methanol has been adopted to reduce complexity of the problem and CPU time. It is found that a small deviation from the Lorentz rule along with a larger change in the Berthelot cross energy gives rise to a concavity of the excess volume at low methanol concentrations and hence to a minimum in the partial molar volume which is otherwise missing if the Lorentz-Berthelot rules are used. Nonetheless, it does not seem that non-Lorentz-Berthelot rules alone will be able to bring the results to a full quantitative agreement with experiment.