X-ray photoelectron spectroscopies (XPS) have become widely used tools to investigate the electronic structure of molecules and materials. Along with the experimental advances in these techniques, reliable interpretation of the XPS spectra requires simulations of core-ionized states using accurate electronic structure methods. However, multireference strongly correlated molecular systems are challenging problems to most theoretical techniques available nowadays. This paper presents a new approach for the XPS simulations combining the multireference algebraic diagrammatic construction theory (MR-ADC) with the core-valence separation technique (CVS).
MR-ADC methods are derived from the expansion of the one-particle Green’s function in a perturbative series, similar to the widely known single-reference ADC, but using a Complete Active Space (CAS) wavefunction as the ground-state reference. We developed the second-order CVS-IP-MR-ADC(2) and its extended version CVS-IP-MR-ADC(2)-X methods and implemented them in the Prism code (to be available soon). In practice, the IP-MR-ADC eigenvalue problem is reduced only to the excitations related to the core ionized states, providing an additional efficiency compared to valence ionization calculations.
We benchmarked the accuracy of CVS-MR-ADC for the K-edge ionization energies of small weakly-correlated molecules against the accurate results from EOM-CCSDT results. As expected, the performance of CVS-MR-ADC methods is similar to the single-reference ADC approximations. It shows the weaker dependence on reference CASSCF orbitals of the extended CVS-IP-MR-ADC(2)-X formulation. However, the CVS-IP-MR-ADC methods are more accurate and reliable for multireference systems, such as the investigated ozone (O3) molecule and the benzynes (C6H4) diradical isomers, in comparison to Multireference Configuration Interaction (MRCI) results as well in the description of experimental measurements.
de Moura, C. E. V., Sokolov, A. Yu. (2022). Simulating X-ray Photoelectron Spectra With Strong Electron Correlation Using Multireference Albegraic Diagrammatic Construction Theory Physical Chemistry Chemical Physics, 24 (8), 4769-4784. https://doi.org/10.1039/D1CP05476G
de Moura, C. E. V., Sokolov, A. Yu. (2022). Correction: Simulating X-ray Photoelectron Spectra With Strong Electron Correlation Using Multireference Albegraic Diagrammatic Construction Theory Physical Chemistry Chemical Physics, 24 (13), 8041-8046. https://doi.org/10.1039/d2cp90053j
Comments are closed.