1. Computational Condensed Matter Physics Laboratory, RIKEN, Wako, Saitama 351-0198, Japan
2. Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
3. CREST, Japan Science and Technology Agency, Chiyoda, Tokyo 100-0075, Japan
4. Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan