1. Key Laboratory of Pharmaceutical Quality Control of Hebei ProvinceCollege of Pharmaceutical SciencesHebei University Baoding 071002 P. R. China
2. Center for Computational Quantum ChemistryUniversity of Georgia Athens GA 30602 USA
3. MOE Key Laboratory of Theoretical Chemistry of the EnvironmentCenter for Computational Quantum ChemistrySouth China Normal University Guangzhou 510006 P. R. China