1. Department of Physics, The Chinese University of Hong Kong, Shatin 999077, Hong Kong SAR, People’s Republic of China
2. Materials Simulation and Modelling, Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600MB Eindhoven, The Netherlands
3. Department of Chemistry, Hong Kong University of Science and Technology, Kowloon 999077, Hong Kong SAR, People’s Republic of China