Ab Initio Calculations of XUV Ground and Excited States for First-Row Transition Metal Oxides

Abstract

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.

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