Institution: | a Institute for Solid State Physics, The University of Tokyo, Kashiwanoha, Kashiwa-shi, Chiba 277-8581, Japan b Center for Advanced Study, Tsinghua University, Beijing 100084, People’s Republic of China c Bremen Center for Computational Materials Science, Universität Bremen, Otto-Hahn-Allee 1, 28359 Bremen, Germany d Department of Physics, Tsinghua University, Beijing 100084, People’s Republic of China |