A new parameterization of the DFT/CIS method with applications to core-level spectroscopy

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Spectroscopy

Background:

• Time-dependent density functional theory (TD-DFT) often underestimates core-to-valence excitation energies due to issues with Rydberg and charge-transfer states.
• Accurate simulation of core-level excitation energies is crucial for interpreting X-ray spectra.

Purpose of the Study:

• To develop an efficient and accurate computational method for simulating X-ray near-edge spectra.
• To address the underestimation of core-to-valence excitation energies in standard TD-DFT calculations.

Main Methods:

• Implementation of an empirically modified configuration interaction with single substitutions (CIS) method based on Kohn-Sham orbitals, termed DFT/CIS.
• Parameter optimization for a specific range-separated hybrid functional to create a black-box method for spectroscopy.
• Calculation of K-edge and L-edge absorption and emission spectra for various elements and transition metals.

Main Results:

• DFT/CIS accurately simulates K-edge absorption and emission spectra for second- and third-row elements and 3d transition metals.
• Promising results were obtained for L-edge spectra.
• DFT/CIS calculations require significantly smaller absolute shifts compared to standard TD-DFT.

Conclusions:

• The developed DFT/CIS method provides a semi-quantitative and efficient approach for simulating X-ray near-edge spectra.
• This method is suitable for complex molecules and materials, offering improved accuracy over standard TD-DFT.
• DFT/CIS is a valuable tool for both core and valence spectroscopy, aiding in spectral interpretation.