Computing L- and M-edge spectra using the DFT/CIS method with spin-orbit coupling

Area of Science:

• Computational Chemistry
• Spectroscopy
• Quantum Mechanics

Background:

• Modeling X-ray spectra, particularly L-edge spectra, necessitates accounting for spin-orbit splitting of 2p orbitals.
• Accurate computation of core-level spectra is essential for understanding electronic structure.

Purpose of the Study:

• To introduce a low-cost computational tool for calculating core-level spectra, specifically addressing L-edge spectra.
• To incorporate spin-orbit splitting effects into the calculation of core-level spectra.

Main Methods:

• Combines a spin-orbit mean-field description of the Breit-Pauli Hamiltonian with nonrelativistic excited states from the semi-empirical density-functional theory configuration-interaction singles (DFT/CIS) method.
• Utilizes a state-interaction approach and a semi-empirical correction to core orbital energies, reducing the need for ad hoc shifts.
• Employs the core/valence separation approximation and spin-orbit couplings.

Main Results:

• The DFT/CIS method, with spin-orbit coupling, provides semiquantitative L-edge spectra at a low computational cost.
• Spin-orbit coupling significantly impacts the calculated spectra, as demonstrated for 3d transition metals and main-group compounds.
• Spin-orbit splitting was found to have a negligible effect on M-edge spectra for 3d transition metal species.

Conclusions:

• The developed DFT/CIS approach offers a computationally efficient and accurate method for modeling L-edge spectra.
• The inclusion of spin-orbit coupling is critical for qualitative agreement in L-edge spectral calculations.
• The tool facilitates spectral assignments through the use of different active orbital spaces.