1. Shanghai Institute of Materia Medica, Chinese Academy of Sciences, No. 501 Haike Road, Shanghai 201203, P. R. China.
2. University of Chinese Academy of Sciences, No. 19A Yuquan Road, Beijing 100049, P. R. China.
3. Laboratory of Theoretical and Computational Nanoscience, Key Laboratory for Nanosystem and Hierarchy Fabrication, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Chinese Academy of Sciences, Beijing 100190, P. R. China.