1. Theoretical Chemistry, Chemical Center, Lund University, POB 124, S-221 00 Lund, Sweden, Physical Chemistry 1, Chemical Center, Lund University, POB 124, S-221 00 Lund, Sweden, LRRS, UMR CNRS 5613, Université de Bourgogne, F-21078 Dijon Cedex, France, and PMMH, ESPCI, 10 rue Vauquelin, F-75231 Paris Cedex 05, France