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

06 May 2025, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Modeling L- and M-edge spectra at x-ray and extreme ultraviolet wavelengths requires consideration of spin-orbit splitting within the 2p and 3p orbital manifolds. We introduce a low-cost tool to compute core-level spectra that combines a spin-orbit mean-field description of the Breit-Pauli Hamiltonian with nonrelativistic excited states computed using the semi-empirical density-functional theory/configuration-interaction singles (DFT/CIS) approach. The latter was previously introduced for K-edge spectra and includes a semi-empirical correction to the core orbital energies, significantly reducing the ad hoc shifts that are typically required when time-dependent (TD-)DFT is applied to core-level excitations. In combination with the core/valence separation approximation and spin-orbit couplings, the DFT/CIS method affords semiquantitative L- and M-edge spectra at TD-DFT cost, as demonstrated here for a variety of 3d transition metal systems and main-group compounds. The use of different active orbital spaces to make spectral assignments is also discussed.

Keywords

core-level spectroscopy
relativistic effects
time-dependent density functional theory
excited states
XANES
x-ray

Supplementary materials

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Description
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coordinates
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Cartesian coordinates for all of the systems examined.
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