1. a Institute of Theoretical Physics, Northeast Normal University , Changchun , 130024 , PR China
2. b The Open Laboratory of Excited State Processes , Changchun Institute of Physics, Academia Sinica , Changchun , 130021 , PR China
3. d Advanced Science and Technology Center for Cooperative Research , Kyushu University , Kasuga Park 6-1, Fukuoka , 816 , Japan
4. c Dipartimento di Fisica , Politecnico di Torino , Duca degli Abruzzi 24, 10129 , Torino , Italy