1. Department of Chemistry, Rutgers University, 610 Taylor Road, Piscataway, NJ 08854, USA
2. Institut für Theoretische Physik, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
3. Theoretical Chemistry, Materials Science Centre, Rijksuniversiteit Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands