1. Department of Materials Science and Engineering, Research Institute of Advanced Materials (RIAM), Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 151-742, Republic of Korea
2. Center for Computational Science, Korea Institute of Science and Technology (KIST), Hwarangno 14-gil 5, Seongbuk-gu, Seoul 136-791, Korea
3. Center for Nanoparticle Research at Institute for Basic Science (IBS), 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea