1. Institute of Theoretical Chemistry, Jilin University, Changchun 130023, People's Republic of China
2. Department of Theoretical Chemistry, Lund University, Chemical Centre, P. O. Box 124, 22100 Lund, Sweden, http://www.teokem.lu.se/~ulf/
3. Institut für Physikalische Chemie, Universität Göttingen, Tammannstrasse 6, 37077 Göttingen, Germany