1. Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, USA
2. Key Laboratory of Computational Physical Sciences (Ministry of Education), State Key Laboratory of Surface Physics, Collaborative Innovation Center of Advanced Microstructures, and Department of Physics, Fudan University, Shanghai 200433, People’s Republic of China
3. Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, People’s Republic of China
4. Max-Planck-Institut für Festkörperforschung, D-70569 Stuttgart, Germany