1. Center
for Computational Science, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea
2. Department
of Materials Science and Engineering, Cornell University, Ithaca, New York 14853, United States
3. Nanomaterials
Science and Engineering, Korea University of Science and Technology, Daejon 305-333, Republic of Korea
4. Department
of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611, United States