1. Department of Applied Physics, Nagoya University, Chikusa, Nagoya 464-8603, Japan.
2. Department of Advanced Science and Engineering, Waseda University, Tokyo 169-855, Japan.
3. Research Center for Computational Design of Advanced Functional Materials (CD-FMat), National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan.
4. Research Institute for Electronic Science, Hokkaido University, Sapporo 001-0020, Japan.