Multi-reference protocol for (auto)ionization spectra: Application to molecules

Voß

Bokarev

et al. 2022

Preprint

Self Cite

A methodology to calculate the decay rates of normal and resonant Auger processes in atoms and molecules based on the One-Center Approximation (OCA) using atomic radial Auger integrals is implemented within the restricted-active-space self-consistent-field (RASSCF) and multi-state restricted-active-space perturbation theory of second order (MS-RASPT2) frameworks as part of the OpenMolcas project. To ensure an unbiased description of the correlation and relaxation effects on the initial core excited/ ionized states and the final cationic states, their wave functions are optimized independently, whereas the Auger matrix elements are computed with a biorthonormalized set of molecular orbitals within the state-interaction (SI) approach. As a decay of an isolated resonance, the computation of Auger intensities involves matrix elements with one electron in the continuum. However, treating ionization and autoionization problems can be overwhelmingly complicated for non-experts because of many peculiarities in comparison to bound-state electronic structure theory. One of the advantages of our approach is that, by projecting the intensities on the atomic center bearing the core hole and using precalculated atomic radial two-electron integrals, the Auger decay rates can be easily obtained directly with OpenMolcas, avoiding the need to interface it with external programs to compute matrix elements with the photoelectron wave function. The implementation is tested on the Ne atom, for which numerous theoretical and experimental data are available for comparison, as well as on a set of prototype closed- and open-shell molecules, namely, CO, N2, HNCO, H2O, NO2, and C4N2H4 (pyrimidine).

Section: The Auger Spherical Symmetric Continuum Approximation (Sci)mentioning

confidence: 99%

“…In the partial-wave expansion, 65 the value l MAX = 10 was used for the singlet and triplet decay channels in NO 2 , as well as in H 2 O. For pyrimidine, l MAX = 17 was applied to reach convergence.…”

Section: Computational Detailsmentioning

confidence: 99%

Multi-Reference Approach to Normal and Resonant Auger Spectra Based on the One-Center Approximation

Voß

Bokarev

et al. 2022

Preprint

Self Cite

“…The RASSI method has been used to compute matrix elements over distinct (biorthonormal) molecular orbital (MO) sets of inner-shell states with great success. [66][67][68] To briefly recapitulate the attributes of the RASSI method, 59,65 let us first write the matrix elements between two distinct optimized wave functions Ψ A and Ψ B described by a CI expansion of Slater determinant functions (SDF) or spin-adapted configuration state functions (CSF), Φ A and Φ B , constructed from the sets of molecular orbitals {φ A } and {φ B } (Ψ A and Ψ B can be generalized to the case of CASSCF or mixed CASPT2 wave-functions)…”

Section: Accurate and Computationally Efficient Ssdch Multi-reference...mentioning

confidence: 99%

Multi-reference approach to the computation of double core-hole spectra

The Journal of Chemical Physics

Decleva

Coriani

2021

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“…The RASSI method has been used to compute matrix elements over distinct (biorthonormal) molecular orbital (MO) sets of inner-shell states with great success [64][65][66] . To briefly recapitulate the attributes of the RASSI method 59,63 , let us first write the matrix elements between two distinct optimized wave functions Ψ A and Ψ B described by a CI expansion of Slater determinant functions (SDF) or spin-adapted configuration state functions (CSF), Φ A and Φ B , constructed from the sets of molecular orbitals {φ A } and {φ B } (Ψ A and Ψ B can be generalized to the case of CASSCF or RASSCF wave-functions)…”

mentioning

confidence: 99%

Communication: Multi-reference Approach to the Computation of Double-Core-Hole Spectra

Decleva

Coriani

2021

Preprint

Double-Core Hole (DCH) states of small molecules are assessed with the restricted active space self-consistent field (RASSCF) and multi-state restricted active space perturbation theory of second order (MS-RASPT2) approximations. To ensure an unbiased description of the relaxation and correlation effects on the DCH states, the neutral ground state and DCH wave functions are optimized separately, whereas the spectral intensities are computed with a biorthonormalized set of molecular orbitals within the state-interaction (SI) approximation. Accurate shake-up satellites binding energies and intensities of double-core-ionized states (K-2) are obtained for H2O, N2, CO and C2H2n (n=1–3). The results are analyzed in detail and show excellent agreement with recent theoretical and experimental data. The K^{-2} shake-up spectra of H2O and the C2H2n molecules are here completely characterized for the first time.