1. Doctoral Program in Materials Science, Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan
2. Center for Computational Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8577, Japan
3. Division of Materials Science, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan