1. Department of Physics, University of North FloridaJacksonvilleFL 32224USA
2. Theoretical Division and Center for Integrated Nanotechnologies, Los Alamos National LaboratoryLos AlamosNM 87545USA
3. Los Alamos National Laboratory, Institute of Material ScienceLos AlamosNM 87545USA
4. Nordic Institute for Theoretical Physics, KTH Royal Institute of Technology and Stockholm UniversityRoslagstullsbacken 2310691 StockholmSweden