1. Department of Chemistry & Key Laboratory of Organic Optoelectronics, and Molecular Engineering of the Ministry of Education Tsinghua University Beijing 100084 P.R. China
2. Institut für Theoretische Chemie Universität Stuttgart Stuttgart 70550 Germany
3. Theoretisch-Physikalisches Institut Universität Jena Jena 07743 Germany
4. Department of Chemistry University of Helsinki, POB 55 Helsinki 00014 Finland
5. Theoretische Chemie, Fachbereich Chemie-Biologie Universität Siegen Siegen 57068 Germany
6. Department of Chemistry Southern University of Science and Technology Shenzhen 518055 P.R. China