Acknowledgements

The author acknowledges M. Saito, S. Tsukimoto, at the WPI Research Center, Advanced Institute for Materials Research, Tohoku University and Y. Ikuhara at the The University of Tokyo for their collaborations. The author thanks S. Watanabe at The University of Tokyo for allowing our use of computational resources. The present study was supported in part by a Grant-in-Aid for Scientific Research on Priority Area, "Atomic Scale Modification (474)" from the Ministry of Education, Culture, Sports, Science, and Technology of Japan. Z. W acknowledges financial supports from the Grant-in-Aid for Young Scientists (A) (Grant No. 24686069) and the Challenging Exploratory Research (Grant No. 24656376). The calculations were carried out on a parallel SR11000 supercomputer at the Institute for Solid State Physics, Univ. of Tokyo.
