1. Department of Chemistry, McMaster University, Hamilton, Ontario L8S 4M1, Canada; Snowbird Software, Inc., 71A Leland Street, Hamilton, Ontario, L8S 3A1, Canada; Department of Chemistry, University of Jyväskylä, P.O. Box 35, FIN-40351 Jyväskylä, Finland; and Max-Planck-Institut für Chemische Physik fester Stoffe, Raum B1.2.11, Nöthnitzer Strasse 40, Dresden D-01187, Germany