Figure shows the calculated O K-edge spectra of three Yb 2 O 3 polymorphs. Here, for monoclinic and hexagonal phases, O K-edge spectra of different oxygen sites are averaged with weighting using atomic fraction. As shown in the figure, the spectra are characterized by twin peaks near the thresholds labeled A and B. The higher energy peak (B) of cubic Yb 2 O 3 is exploited as the origin point of the theoretical spectra in this study; this is because the relative peak positions are meaningful and comparable to experimental results .