1. School of Engineering and Technology, Neijiang Normal University, Neijiang, Sichuan 641112, P. R. China
2. College of Physical Science and Technology, Sichuan University, Chengdu, Sichuan 610064, P. R. China
3. School of Physical Science and Technology, Southwest Jiaotong University, Chengdu 610031, P. R. China
4. Center for Computational Quantum Chemistry, University of Georgia, Athens, GA 30602, USA, http://www.ccqc.uga.edu