1. Physics Department and Institute for Nanoscience and Engineering, University of Arkansas, Fayetteville, Arkansas, USA;
2. Mathematics Department, University of Arkansas, Fayetteville, Arkansas, USA;
3. Department of Theoretical Materials Physics, Q-MAT CESAM, Université de Liège, Sart Tilman, Belgium;
4. Departments of Materials Science and Engineering, University of Delaware, Newark, Delaware, USA;
5. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA