The O K-edge spectra were simulated using the supercell core-hole method . The number of unoccupied orbitals was increased enough to obtain an energy up to 30 eV above the threshold. Each spectrum was smeared with the Gausian function with a smearing width of 0.8 eV. Information on crystal structure and k-point grids for the Brillouin zone (BZ) sampling of each compound are presented in the following sections. Local atomic structures are depicted by the VESTA code .