X-ray absorption spectroscopy of titanium oxide by time dependent density functional calculations

Area of Science:

• Computational materials science
• Quantum chemistry
• Solid-state physics

Background:

• Transition metal oxides exhibit complex electronic structures.
• Core excitation spectra (XAS) provide crucial insights into electronic properties.
• Accurate theoretical methods are needed to interpret experimental XAS data.

Purpose of the Study:

• To evaluate the efficacy of time-dependent density functional theory (TDDFT) for simulating XAS in transition metal oxides.
• To assess TDDFT performance using rutile TiO2 as a model system.
• To compare theoretical predictions with experimental XAS data across different absorption edges.

Main Methods:

• Utilized cluster models embedded in point charge arrays to simulate the Madelung potential of bulk TiO2.
• Calculated titanium (Ti) and oxygen (O) K-edges, and Ti L-edges using TDDFT.
• Compared TDDFT results with experimental XAS data.
• Investigated spectral features using partial density of virtual states (PDOS).

Main Results:

• TDDFT accurately reproduced experimental XAS for Ti and O K-edges.
• Discrepancies were observed between TDDFT and experimental data for the Ti L-edge.
• Configuration mixing in TDDFT significantly impacted the distribution of 2p metal oscillator strength.
• PDOS analysis aided in understanding the origin of spectral features.

Conclusions:

• TDDFT is a promising approach for describing core excitation spectra in transition metal oxides, particularly for K-edges.
• Further methodological development is needed to improve TDDFT accuracy for L-edges.
• The study highlights the importance of configuration mixing and PDOS analysis in interpreting XAS.