1. Department of Physics, Hong Kong University of Science and Technology, Hong Kong, China
2. Université de Lorraine & CNRS, Laboratoire de Physique et Chimie Théoriques (LPCT), F-54000 Nancy, France
3. Department of Chemistry, The Hong Kong University of Science and Technology, Hong Kong, China
4. HKUST Fok Ying Tung Research Institute, Guangzhou 511458, China