1. Key Laboratory of Chemical Biology and Traditional Chinese Medicine Research, Ministry of Education of China), Hunan Normal University, Changsha, Hunan 410081, P. R. China
2. Qingdao Institute for Theoretical and Computational Sciences, Institute of Frontier and Interdisciplinary Science, Shandong University, Qingdao, Shandong 266237, P. R. China
3. Research Computing Center, University of North Carolina, Chapel Hill, NC 27599-3420, USA
4. Department of Chemistry, University of North Carolina, Chapel Hill, NC 27599-3290, USA