Coupled cluster study of the x-ray absorption spectra of formaldehyde derivatives at the oxygen, carbon, and fluorine K-edges

Abstract

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XABOOM: An X-Ray Absorption Benchmark of Organic Molecules Based on Carbon, Nitrogen, and Oxygen 1s → π ∗ Transitions

“…54,58 With this, CC has been successfully applied to describe XAS spectra for small and medium-sized molecules, showing a high accuracy in comparison to experimental data. 34,35,40,43,53,110,145 Molecular systems and selected states…”

“…As such, the results presented here are compared to reference values obtained using EOM-CCSD and ADC(2)-x, two methods which have been shown to yield good agreement with experiments on top of having a solid theoretical foundation. 24,36,43,[51][52][53][54][55][56][57][58][59] Note that these methods yield accurate relative features, albeit with element-dependent absolute errors-as an example, the discrepancies with respect to experiment for CO/HCN/CO amounts to approximately −0.1/−0.6/−1.1 eV for ADC(2)-x, and 0.3/0.7/1.2 eV for EOM-CCSD, with relativistic effects accounted for.…”

“…Of note is the work of Besley and Asmuruf, 33 who investigated the performance of TDDFT for core properties and the construction of functionals with reasonable absolute energies, as well as numerous smaller studies for different methods. [34][35][36][37][38][39][40][41][42][43][44] In order to accurately model core-excitation processes, the inclusion of electron relaxation effects is vital. This requires a theoretical method capable of capturing two physical effects: a reduced screening of the probed nuclei following the removal of a core electron, leading to a strong net attraction of the electron density towards the core, and a smaller repulsive polarisation effect in the valence region due to the interaction with the excited electron.…”

“…An abundance of methodologies for modeling X-ray absorption spectra has been developed, including semi-empirical, density-based, and wave function-based methods. 31,33,34,[36][37][38][39]43,45,[49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68] Here the focus is on first-principles methods, and hence semi-empirical approaches will thus be left out of the discussion. Among the first-principles methods, researchers in the field of theoretical spectroscopy commonly apply density functional theory (DFT).…”

Equation-of-Motion Coupled-Cluster Theory to Model L-edge X-Ray Absorption and Photoelectron Spectra

“…This idea, which provides a simple recipe for extending methods targeting valence states into the core-level domain, has been implemented within various electronic structure methods, [16][17][18][19][20][21] including the EOM-CC family. [22][23][24] The resulting methods have been successfully applied to model a variety of x-ray spectroscopic experiments such as absorption (XAS), 22,23,25,26 photoelectron (XPS), 24,27,28 x-ray emission (XES) and resonant inelastic scattering (RIXS). 14, [29][30][31] At the CC level, the applications have been so far limited to the study of 1s electrons of light elements (that is, the K-edge), due to yet another obstacle towards the quantitative simulation of x-ray spectra-the need to include relativistic effects.…”