We would like to thank Tijana Milenković for providing the softwares of DS-DC and DS-GDC. We would like to thank the associate editor and the anonymous reviewers for their helpful suggestions which have brought improvement of this work. This work is partially supported by the National Science Foundation of China [61402190, 11401110, 61402276, 61375033, 11171354], the Ministry of Education of China [20120171110016], the Natural Science Foundation of Guangdong Province [S2013020012796, 2013KJCX0086], the International Program Fund of 985 Project, Sun Yat-sen University, and self-determined research funds of CCNU from the colleges’ basic research and operation of MOE [CCNU15A05039].