First-principles calculations for XAS of infinite-layer iron oxides

The oxygen defect perovskite SrFeO$_{3-x}$ shows various properties such as the giant magnetoresistance effect and the thermoelectric effect. It had been believed that the oxygen content in SrFeO$_{3-x}$ changes up to $x=0.5$. Recently, Tsujimoto $et$ $al.$ have succeeded in synthesizing the infinite-layer iron oxide SrFeO$_2$. SrFeO$_2$ has a square-planar oxygen coordination, while the iron oxides usually have the tetrahedral and octahedral coordination. CaFeO$_2$ has also infinite layer structure and the same magnetic ordering as SrFeO$_2$. However, it is suggested that the oxygen coordination of CaFeO$_2$ is different from that of SrFeO$_2$. In order to investigate the electronic structure of iron in (Ca, Sr)FeO$_2$, the x-ray absorption spectroscopy (XAS) spectrum has been measured. In this work, we perform the calculation for XAS spectrum near the Fe-K edge of (Ca, Sr)FeO$_2$ using the first-principles calculations. We compare the results with the experiment and discuss the electronic structure of iron in (Ca, Sr)FeO$_2$.