1. Department of Physics and Nanotechnology Research and Computation Center, Western Michigan University, Kalamazoo, MI 49008, U.S.A.
2. Computational Condensed-Matter Physics Laboratory, RIKEN ASI, Wako, Saitama 351-0198, Japan
3. Asia Pacific Center for Theoretical Physics, Pohang, Gyeongbuk 790-784, Republic of Korea