1. State Key Laboratory of Electrical Insulation and Power Equipment, Xi’an Jiaotong University, Xi’an, Shaanxi Province 710049, China
2. State Grid Sichuan Electric Power Research Institute, Chengdu, Sichuan Province 610041, China
3. Mulliken Center for Theoretical Chemistry, Institute of Physical and Theoretical Chemistry, University of Bonn, Beringstr. 4, 53115 Bonn, Germany