1. Laboratoire de Chimie Théorique, CNRS, Université Pierre et Marie Curie, 4 Place Jussieu, 75252 Paris, France, Afdeling Theoretische Chemie, Vrije Universiteit, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands, Department of Physics and Astronomy, University of Missouri, Columbia, Missouri 65211, and Institute of Theoretical Physics, University of Regensburg, 93040 Regensburg, Germany