1. Department of Mechanical Science and Engineering, NSF Center for Novel High Voltage/Temperature Materials and Structures, Institute for Condensed Matter Theory, and Beckman Institute, University of Illinois at Urbana-Champaign, Champaign, Urbana 61801, USA
2. National Center for Supercomputing Applications, University of Illinois at Urbana-Champaign, 1205 W. Clark St., Urbana, Illinois 61801, USA