X-ray absorption spectroscopy (XAS) is an element specific probe that has been used to understand the local electronic and binding environment around metal centers, such as describing oxidation states, differential orbital covalency, and local site symmetry. Electronic structure theory has become an important aid in interpreting X-ray absorption spectra; however, the abilities of newly developed techniques to model the near-edge region of XAS have not yet been fully determined. While K-edge spectra have been investigated in great detail, the modeling of L-edge spectra poses several unique challenges. First, the L-edge spectrum is composed of multiple features: L1 corresponding to the 2s orbital, and L2,3 corresponding to 2p orbitals, which are split into 2p1/2 and 2p3/2 levels by spin-orbit coupling. Additionally, with density functional theory (DFT) it also becomes necessary to make modifications to handle non-collinear spin densities in the presence of spin-orbit coupling. We model the L2,3 spectra for several molecules with variety of model chemistries using X2C-TDDFT. With the exact two component (X2C) method we are able to include the one-electron spin-orbit coupling terms variationally from first principles. An analysis of the molecular orbitals involved in the transitions yields valuable theoretical information that can be used to connect the local electronic structure with experimental observables.

Modeling X-ray absorption spectroscopy with TDDFT

256th National Meeting (2018)

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