[1] Seoul Natl Univ, Ctr Strongly Correlated Mat Res, Seoul 151742, South Korea
[2] Ewha Womans Univ, Dept Phys, Seoul 120750, South Korea
[3] USN, Res Lab, Ctr Computat Mat Sci, Washington, DC USA
[4] Seoul Natl Univ, Dept Phys, Seoul 130743, South Korea