1. Departament de Química Inorgànica and Centre de Recerca en Química Teòrica, Universitat de Barcelona, Martí i Franquès 1-11, 08028 Barcelona, Spain, National Institute for Nanotechnology, National Research Council of Canada, 421 Saskatchewan Drive, Edmonton, Alberta, T6G 2M9, Canada, Department of Mechanical Engineering, University of Alberta, Edmonton, Alberta, T6G 2G8, Canada, and Department of Chemistry, University of Calgary, Calgary, Alberta, T2N 1N4, Canada