Relativistic Orbital-Optimized Density Functional Theory for Accurate Core-Level Spectroscopy.

Area of Science:

• Quantum Chemistry
• Spectroscopy
• Computational Materials Science

Background:

• Relativistic effects significantly influence core-level spectra (1s electrons) in elements heavier than Neon.
• Accurate theoretical prediction of these spectra is crucial for understanding electronic structure and chemical properties.

Purpose of the Study:

• To investigate the accuracy of combining orbital-optimized density functional theory (OO-DFT) with the spin-free exact two-component (X2C) model for calculating K-edge spectra of third-period elements.
• To compare the performance of OO-DFT/X2C against the time-dependent DFT (TDDFT) approach.

Main Methods:

• Utilized orbital-optimized density functional theory (OO-DFT) coupled with the spin-free exact two-component (X2C) model.
• Applied the method to calculate K-edge spectra of third-period elements using modern SCAN and related functionals.
• Explored K and L edges of 3d transition metals to assess limitations.

Main Results:

• The OO-DFT/X2C approach demonstrated high accuracy, achieving a root-mean-square error of approximately 0.5 eV compared to experimental data.
• This represents a substantial improvement over TDDFT, which typically shows deviations exceeding 50 eV.
• Experimental spectra were well-reproduced by OO-DFT/X2C without empirical alignment shifts.

Conclusions:

• OO-DFT/X2C offers a computationally efficient and highly accurate method for predicting core-level spectra of third-period elements.
• The approach shows promise for broader applications in computational spectroscopy.
• Identified limitations for modeling spectra of heavier atoms, particularly 3d transition metals.