This work was supported by the National Research Foundation grants to M.Y. Choi (2013R1A1A2057784, 2012R1A2A2A02013289), with the main calculations carried out by the supercomputer facility of the Korea Institute of Science and Technology Information (KSC-2012-C2-46). This work was also supported by the National Research Foundation of Korea through the Star Faculty Program (2012055313) and the Global Frontier R&D Program on Center for Multiscale Energy System (2011-0031567). We also acknowledge the SNU Brain Fusion Grant.