1. Key Laboratory of Cryogenics; Technical Institute of Physics and Chemistry; Chinese Academy of Sciences; Beijing 100190 P. R. China
2. University of Chinese Academy of Sciences; Beijing 100049 P. R. China
3. Beijing Computational Science Research Center; Beijing 100193 China
4. State Key Laboratory of New Ceramics and Fine Processing; School of Materials Science and Engineering; Tsinghua University; Beijing 100084 P. R. China