1. Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
2. Department of Physics, Nanoscience Center, University of Jyväskylä, Jyväskylä 40014, Finland
3. Computational Sciences and Engineering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
4. Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States