1. Department of Materials Science and Engineering, University of Illinois Urbana-Champaign 1 , Urbana, Illinois 61801, USA
2. Materials Research Laboratory, University of Illinois Urbana-Champaign 2 , Urbana, Illinois 61801, USA
3. Materials Science Division, Argonne National Laboratory 3 , Lemont, Illinois 60439, USA
4. Department of Physics, University of Illinois Urbana-Champaign 4 , Urbana, Illinois 61801, USA
5. National Center for Supercomputing Applications, University of Illinois Urbana-Champaign 5 , Urbana, Illinois 61801, USA