Automated exploration of stable isomers of H(+)(H(2)O)(n) (n = 5-7) via ab initio calculations: An application of the anharmonic downward distortion following algorithm.

Isomers of protonated water clusters H(+)(H(2)O)(n) (n = 5-7) have been explored on ab initio potential energy surfaces by means of the anharmonic downward distortion following algorithm. Totally, 9, 24, and 131 isomers for n = 5, 6, and 7, respectively, were located by the automatic exploration, and all of known important isomers previously reported by conventional geometry optimization approaches have been included in the present results. Moreover, structure transitions depending on n and temperature, which were observed by experimental studies, could be reproduced via thermodynamic simulation on the basis of the superposition approach and the present isomer sets. (c) 2008 Wiley Periodicals, Inc.