EFFICIENT ALGORITHM FOR QUANTITATIVE ASSESSMENT OF SIMILARITIES AMONGATOMS IN MOLECULES

A new algorithm for quantitative assessment of similarity between two atoms in molecules is presented. Both the atomic similarity index and its derivatives with respect to the three Euler angles that describe t he mutual orientation of the atoms under comparison are computed effic iently by taking advantage of the recently developed analytical repres entations for atomic zero-flux surfaces. The use of such representatio ns makes it possible to substantially enhance the accuracy of the comp uted similarity indices without increasing the cost of their evaluatio n. Numerical tests involving oxygen atoms in several carbonyl compound s demonstrate the ability of the new algorithm to discern small change s in atomic similarity that are brought about by second-neighbor effec ts. Comparisons among hydrogen atoms in the acrolein molecule reveal t he usefulness of the similarity index in detection and quantification of the effects of steric interactions on atomic shapes. (C) 1996 by Jo hn Wiley & Sons, Inc.