1. The Lundbeck Foundation Center for Theoretical Chemistry, University of Aarhus, Langelandsgade 140, DK-8000 Århus C, Denmark
2. Centre for Theoretical and Computational Chemistry, University of Tromsø, N-9037 Tromsø, Norway
3. Department of Theoretical Chemistry, The Royal Institute of Technology SE-10691 Stockholm, Sweden
4. Dipartimento di Scienze Chimiche, Università degli Studi di Trieste via L. Giorgieri 1, I-34127 Trieste, Italy, and Centre for Theoretical and Computational Chemistry, University of Oslo, P.O. Box 1033 Blindern, N-0315 Oslo, Norway