Computer simulation of acetonitrile and methanol with ab initio-based pairpotentials

This study address the adequacy of ab initio pair interaction energy potent ials for the prediction of macroscopic properties. Recently, Bukowski [J. P hys. Chem. A 103, 7322 (1999)] performed a comprehensive study of the poten tial energy surfaces for several pairs of molecules using symmetry-adapted perturbation theory. These ab initio energies were then fit to an appropria te site-site potential form. In an attempt to bridge the gap between ab ini tio interaction energy information and macroscopic properties prediction, w e performed Gibbs ensemble Monte Carlo (GEMC) simulations using their devel oped pair potentials for acetonitrile and methanol. The simulations results show that the phase behavior of acetonitrile is well described by just the pair interaction potential. For methanol, on the other hand, pair interact ions are insufficient to properly predict its vapor-liquid phase behavior, and its saturated liquid density. We also explored simplified forms for rep resenting the ab initio interaction energies by refitting a selected range of the data to a site-site Lennard-Jones and to a modified Buckingham (expo nential-6) potentials plus Coulombic interactions. These were also used in GEMC simulations in order to evaluate the quality and computational efficie ncy of these different potential forms. It was found that the phase behavio r prediction for acetonitrile and methanol are highly dependent on the deta ils of the interaction potentials developed. (C) 2000 American Institute of Physics. [S0021-9606(00)51137-4].