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Published July 20, 2022 | Supplemental Material
Journal Article Open

Ab Initio Prediction of Excited-State and Polaron Effects in Transient XUV Measurements of α-Fe₂O₃

Abstract

Transient X-ray and extreme ultraviolet (XUV) spectroscopies have become invaluable tools for studying photoexcited dynamics due to their sensitivity to carrier occupations and local chemical or structural changes. One of the most studied materials using transient XUV spectroscopy is α-Fe₂O₃ because of its rich photoexcited dynamics, including small polaron formation. The interpretation of carrier and polaron effects in α-Fe₂O₃ is currently carried out using a semi-empirical method that is not transferrable to most materials. Here, an ab initio, Bethe-Salpeter equation (BSE) approach is developed that can incorporate photoexcited-state effects into arbitrary material systems. The accuracy of this approach is proven by calculating the XUV absorption spectra for the ground, photoexcited, and polaron states of α-Fe₂O₃. Furthermore, the theoretical approach allows for the projection of the core-valence excitons and different components of the X-ray transition Hamiltonian onto the band structure, providing new insights into old measurements. From this information, a physical intuition about the origins and nature of the transient XUV spectra can be built. A route to extracting electron and hole energies is even shown possible for highly angular momentum split XUV peaks. This method is easily generalized to K, L, M, and N edges to provide a general approach for analyzing transient X-ray absorption or reflection data.

Additional Information

© 2022 American Chemical Society. Received: April 13, 2022; Published: July 11, 2022. I.M.K. was supported by an NSF Graduate Research Fellowship (DGE-1745301). H.L. and D.N. were supported by the Liquid Sunlight Alliance, which is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Fuels from Sunlight Hub under Award Number DE-SC0021266. Author Contributions. All authors have given approval to the final version of the manuscript. The authors declare no competing financial interest.

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Created:
August 22, 2023
Modified:
October 24, 2023