1. Contribution from the Department of Chemistry, State University of New York at Buffalo, Buffalo, New York 14260, Departamento de Química Física, Universidad de Extremadura, 06071 Badajoz, Spain, Departament de Química, Universitat Autònoma de Barcelona, 08193 Bellaterra (Barcelona), Spain, and Department of Chemistry and Supercomputer Institute, University of Minnesota, Minneapolis, Minnesota 55455