Using DV X α method, we calculated electronic structures of (Fe 3+ O 2- 6) 9- and (Fe 3+ O 2- 4) 5- clusters of YIG. We found that only crystal field transitions exist in (Fe 3+ O 2- 6) 9- cluster under 3.5eV, and that charge transfer transitions exist in (Fe 3+ O 2- 4) 5- cluster around 3.5eV. In the wave number from 12×10 5 m -1 to 25×10 5 m -1 , we calculated the optical absorption spectra wh...