1. Institute for Condensed Matter Theory and Department of Chemistry, Chonnam National University, 300 Yongbong-Dong, Bukgu, Gwangju 500-757, Korea, Electronic Materials Laboratory, Samsung Advanced Institute of Technology, P. O. Box 111, Suwon 440-600, Korea, and Department of Chemistry and Institute of Basic Science, Chonnam National University, 300 Yongbong-Dong, Bukgu, Gwangju 500-757, Korea