1. Department of Physics, National Central University, Jhongli 32001, Taiwan
2. Chemical Physics Theory Group, Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada
3. Abteilung Physikalische Chemie, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany
4. Institute of Physics, Academia Sinica, Taipei 11520, Taiwan
5. Physics Division, National Center for Theoretical Sciences, Hsinchu 30013, Taiwan