1. Computational Sciences and Engineering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6164, USA.
2. Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6124, USA.
3. Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6062, USA.
4. Department of Materials Science and Engineering, Michigan Technological University, Houghton, MI 49931, USA.