1. Department of Physics and Astronomy and Center for Simulational Physics, University of Georgia, Athens, Georgia 30602, United States
2. Key Laboratory of Materials Modification by Laser, Electron, and lon Beams (Ministry of Education), School of Physics, Dalian University of Technology, Dalian 116024, P. R. China
3. Department of Chemistry and Biochemistry, University of Nevada, Las Vegas, Nevada 89154, United States
4. Theoretical Division (T-1, MS B221), Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States