Nearly ab-initio MLFT applied to Kα XES of 3d transition metal oxides

Accurate first-principles predictions of the excited states and spectra of 3d transition metals have historically been challenging due to their highly correlated nature. Model based approaches such as multiplet ligand field theory (MLFT) have been successful in describing the spectra of such systems, but have limited predictive capability due to the large number of free parameters. Recent work combines density functional theory (DFT) with MLFT to obtain many of these parameters, and has been been applied to the x-ray absorption and valence to core emission of a wide variety of materials. However, there are few applications of this approach to core-to-core emission. Here we present an extension of the DFT plus MLFT approach of Haverkort et al. [1] within the code Quanty, to achieve a nearly ab-initio calculation of core-to-core X-ray Emission Spectroscopy (XES) of these materials. In this approach, a tight binding (TB) Hamiltonian describing the crystal field splitting as well as coupling to the ligand states is extracted from the DFT calculation. The 2-particle Coulomb interaction (Slater-Condon) parameters are also calculated within DFT, taking into account the nephelauxatic reduction. We demonstrate promising agreement between experiment and theory across a range of transition metals (Cr, Mn, and Ni), as well as the ability to reproduce key spectral trends which are dependent on oxidation state, spin state, and coordination geometry. Finally, we investigate the dependence of the spectra on the remaining free parameters to demonstrate the merits and limitations of the approach.