Possible crystal structures of acetic acid were generated, considering
eight space groups and assuming one molecule in the asymmetric unit.
Our grid-search method was compared with a Monte Carlo approach as imp
lemented in the Biosym/MSI Polymorph Predictor. This revealed no sampl
ing deficiencies. A large number of possible crystal structures were f
ound (similar to 100 within only 5 kJ/mol), including the experimental
structure. Energy minimizations were done with a united-atoms force f
ield (GROMOS), an all-atoms force field (AMBER), and a potential that
describes the electrostatic interactions with distributed multipoles (
DMA). In all cases, the experimental structure had a low lattice energ
y. The number of hypothetical crystal structures was reduced considera
bly by removing space-group symmetry constraints, or by a primitive mo
lecular dynamics shake-up. Nevertheless, sufficient structures of equa
l or lower energy compared with the experimental structure remained to
suggest that other factors need to be considered for genuine structur
e prediction. (C) 1998 John Wiley & Sons, Inc.