Ab Initio Calculations of XUV Ground and Excited States for First-Row Transition Metal Oxides
Transient X-ray spectroscopies have become ubiquitous in studying photoexcited dynamics in solar energy materials due to their sensitivity to carrier occupations and local chemical or structural dynamics. The interpretation of solid-state photoexcited dynamics, however, is complicated by the core–hole perturbation and the resulting many-body dynamics. Here, an ab initio, Bethe–Salpeter equation (BSE) approach is developed that can incorporate photoexcited state effects for solid-state materials. The extreme ultraviolet (XUV) absorption spectra for the ground, photoexcited, and thermally expanded states of first row transition metal oxides─TiO₂, α-Cr₂O₃, β-MnO₂, α-Fe₂O₃, Co₃O₄, NiO, CuO, and ZnO─are calculated to demonstrate the accuracy of this approach. The theory is used to decompose the core–valence excitons into the separate components of the X-ray transition Hamiltonian for each of the transition metal oxides investigated. The decomposition provides a physical intuition about the origins of XUV spectral features as well as how the spectra will change following photoexcitation. The method is easily generalized to other K, L, M, and N edges to provide a general approach for analyzing transient X-ray absorption or reflection data.
© 2023 American Chemical Society. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the United States Air Force. The computations presented here were conducted in the Resnick High Performance Computing Center. This material is based upon work supported by the Air Force Office of Scientific Research under award number FA9550-21-1-0022. I.M.K. was supported by an NSF Graduate Research Fellowship (DGE-1745301). W.L. was supported by the Korea Foundation for Advanced Studies (KFAS) Graduate Research Fellowship. The Resnick High Performance Computing Center is a facility supported by the Resnick Sustainability Institute at the California Institute of Technology. Author Contributions. All authors have given approval to the final version of the manuscript. The authors declare no competing financial interest.