Kohn-Sham density functional theory calculations of non-resonant and resonant x-ray emission spectroscopy

Abstract

The effect of basis set and exchange-correlation functional on time-dependent density functional theory calculations within the Tamm The accuracy of non-resonant and resonant (resonant inelastic X-ray scattering) X-ray emission spectra simulated based upon Kohn-Sham density functional theory is assessed. Accurate non-resonant X-ray emission spectra with the correct energy scale are obtained when short-range corrected exchangecorrelation functionals designed for the calculation of X-ray absorption spectroscopy are used. It is shown that this approach can be extended to simulate resonant inelastic X-ray scattering by using a reference determinant that describes a core-excited state. For this spectroscopy, it is found that a standard hybrid functional, B3LYP, gives accurate spectra that reproduce the features observed in experiment. However, the ability to correctly describe subtle changes in the spectra arising from different intermediate states is more challenging and requires averaging over conformations from a molecular dynamics simulation. Overall, it is demonstrated that accurate non-resonant and resonant X-ray emission spectra can be simulated directly from Kohn-Sham density functional theory.

Zinc 1s Valence-to-Core X-ray Emission Spectroscopy of Halozincate Complexes

“…where φ c is a core orbital with energy ǫ c and φ v is a valence orbital with energy ǫ v , and this and related approaches have been applied to study transition metal complexes. 4,31 Following ionisation of a core electron there will be some relaxation of the electronic structure. This can be included in the calculations through the use of the Z+1 approximation where an increased nuclear charge is used for the absorbing atom 6 or through the transition potential approach where a half filled core orbital is used providing a balance between final and initial states.…”

“…Spectra are also computed based upon Kohn-Sham DFT calculations using equations 1 and 2. For these calculations the SRC1R1 functional was used, 46 following previous work, 31 performed with the Q-CHEM software package 47 except the calculations to determine the quadupole contribution to the oscillator strengths which were performed using the ORCA software. 48,49 Computational spectra were generated by convoluting the computed energies and oscillator strengths with gaussian functions with full-width at half maximum of 0.25 eV.…”

“…An energy shift is derived for the Kohn-Sham DFT spectra in an analogous way to TDDFT, giving an energy shift of +4.0 eV. This shift is much smaller because of the different computational approach and the nature of the SRC1R1 functional used 31. In the calculated spectra the zinc d orbital band has been incorporated by evaluating the intensity of these transitions.…”

Ab initio simulations of x-ray emission spectroscopy with the GW+ Bethe-Salpeter equation method

“…It is important to perform predictive XES calculations, which match experimental spectral features and absolute energies. In recent years, ab initio calculation methods for the XES process have been developed [7][8][9][10][11][12][13] .…”

Assessment of basis sets for density functional theory-based calculations of core-electron spectroscopies

“…TDDFT and EOM-CCSD methods have also been used to study X-ray emission spectroscopy through the use of a reference determinant with a core-hole [20][21][22][23]. More recently, resonant inelastic X-ray scattering spectra have been simulated based upon multi-reference wavefunction methods [24] and also using Kohn-Sham density functional theory with a core-excited reference determinant [25].…”