Project
High-Throughput Calculations of Transition Metal K-and L-Edge X-ray Absorption and Photoemission Spectroscopy
This project aims to develop and apply computational workflows for K-edge and L-edge X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and related dichroic spectroscopies of transition-metal oxides. These materials are important for electronic, magnetic, catalytic, and energy-related applications, but their spectra are often difficult to interpret because several effects contribute at the same time. The main motivation is to understand how local crystal fields, ligand-metal hybridization, charge fluctuations, multiplet interactions, and magnetic order influence experimentally measured spectra. During this reporting period, the work focused on validating the workflow on representative Fe-based oxides, especially hematite α-Fe2O3 and Fe-doped BaTiO3. These systems provide useful test cases because they involve strong electronic correlations, magnetic effects, mixed valence, and complex X-ray spectral features.
Project Details
Project term
April 1, 2025–March 31, 2026
Affiliations
TU Darmstadt
Institute
Theory of Magnetic Materials
Principal Investigator
Methods
The project used a combination of first-principles electronic-structure methods and many-body spectroscopy calculations. DFT and DFT+U calculations were performed to obtain electronic structures and local orbital information. FPLO was used to construct Wannier-based tight-binding Hamiltonians for Fe 3d and O 2p states, which were then used as input for multiplet ligand-field calculations with Quanty. Charge-self-consistent DFT+DMFT calculations were also performed for correlated Fe-based systems in order to include local electronic correlations and finite-temperature effects. For spectroscopy, Quanty was used to calculate XAS, XPS, and XMCD spectra based on local atomic and ligand-field Hamiltonians. The Siesta RT-TDDFT/CORVUS workflow for charge-fluctuation contributions was tested, but could not be fully applied because of a software-compatibility problem described below.
Results
The project produced two main scientific outcomes during this period. First, we studied the altermagnetic material hematite α-Fe2O3. The calculations show that the altermagnetic spin splitting is robust against spin-orbit coupling and finite-temperature electronic correlations. Using DFT combined with multiplet ligand-field theory, we calculated the Fe L2,3-edge XAS and XMCD spectra and identified characteristic XMCD line shapes that can distinguish altermagnetic contributions from weak-ferromagnetic effects.
Second, we investigated the redox behavior of Fe impurities in BaTiO3 using DFT-based many-body calculations. The results show that Fe impurities exhibit mixed-valence character, mainly involving Fe2+ and Fe3+ configurations. Oxygen vacancies shift the valence distribution toward Fe2+, showing that vacancy formation promotes reduction of the Fe impurity. Wannier-derived crystal-field and multiplet calculations were used to evaluate XPS/XAS spectra and compare with experimental observations
Discussion
Overall, the project successfully validated the core computational spectroscopy strategy on representative transition-metal oxide systems. The FPLO/Quanty and DFT+DMFT-based workflows proved effective for describing local multiplet physics, magnetic effects, and X-ray spectroscopic signatures in Fe-based oxides. These results provide a solid basis for extending the calculations toward a broader library of 3d transition-metal oxides.
A technical challenge was encountered in the Siesta/CORVUS part of the workflow. The newer Siesta version available during the project was not directly compatible with the CORVUS interface because CORVUS uses older Siesta input keywords. As a result, the required potentials could not be generated correctly and the planned charge-fluctuation/cumulant calculations could not be completed. Therefore, the main progress during this reporting period focused on the FPLO/Quanty and DFT+DMFT/MLFT parts of the workflow.
Additional Project Information
DFG classification: 406 Materials Science
Software: VASP, FPLO, Wien2k, FEFF10, Quanty
Cluster: CLAIX
Publications
Zhiyuan Li, Hamza Zerdoumi, Hao Wang, Ruiwen Xie, Hongbin Zhang,
Redox behaviour of Fe impurities in BaTiO3 based on many-body calculations,
https://dx.doi.org/10.48550/arXiv.2605.24747, May 2026
Ruiwen Xie, Hamza Zerdoumi, Hongbin Zhang,
X-ray magnetic circular dichroism of altermagnet 𝛼−Fe2O3 based on multiplet ligand-field theory using Wannier orbitals,
https://dx.doi.org/10.1103/4cbj-w8wd, June 2926