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].