1. Center for Integrated Nanotechnologies, Materials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
2. Department of Physics, University of Houston, Houston, Texas 77204, United States
3. Department of Chemistry, University of Houston, Houston, Texas 77204, United States
4. Department of Chemistry and the Smalley-Curl Institute, Rice University, Houston, Texas 77005, United States
5. Department of Materials Science and NanoEngineering, Rice University, Houston, Texas 77005, United States
6. Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States