1. Institute of Theoretical Chemistry, Shandong University, Jinan, 250100, P. R. China, Laboratory for Computational Biology, Shandong Provincial Research Center for Bioinformatic Engineering and Technique, Shandong University of Technology, Zibo, 255049, P. R. China, and Department of Chemistry, Shandong Teachers' University, Jinan, 250014, P. R. China