1. Dipartimento di Chimica Generale ed Organica Applicata, Università di Torino, C.so M. d'Azeglio 48, I-10125 Torino, Italy, Department of Physical Chemistry, Sciences II University of Geneva, 30 Quai Ernest Ansermet, CH-1211 Geneva 4, Switzerland, and Department of Chemistry and Supercomputer Institute, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55455-0431