1. CAS Center for Excellence in Nanoscience, Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing 100083, P. R. China
2. School of Nanoscience and Technology, University of Chinese Academy of Sciences, Beijing 100049, P. R. China
3. Center on Nanoenergy Research, School of Physical Science and Technology, Guangxi University, Nanning 530004, P. R. China
4. Beijing Computational Science Research Center, Beijing 100193, P. R. China
5. Innovative Center for Advanced Materials, Hangzhou Dianzi University, Hangzhou 310018, P. R. China
6. Nanotechnology Research Centre, National Research Council Canada (NRC), Edmonton, Alberta T6G 2M9, Canada