Multireference quantum chemistry protocol for simulating autoionization spectra: Test of ionization continuum models for the neon atom

Abstract

In this contribution we present a protocol to evaluate partial and total Auger decay rates combining the restricted active space self-consistent field electronic structure method for the bound part and numerically obtained continuum orbitals in the single-channel scattering theory framework. On top of that, the two-step picture is employed to evaluate the partial rates. The performance of the method is exemplified for the prototypical Auger decay of the neon 1s −1 3p resonance. Different approximations to obtain the continuum orbitals, the partial rate matrix elements, and the electronic structure of the bound part are tested against theoretical and experimental reference data. It is demonstrated that the partial and total rates are most sensitive to the accuracy of the continuum orbital. For instance, it is necessary to account for the true direct Coulomb potential of the ion for the determination of the continuum wave functions. The Auger energies, however, can be reproduced quite well already with a rather small active space. Finally, perspectives of the application of the proposed protocol to molecular systems are discussed. arXiv:1905.05785v1 [physics.chem-ph]

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

“…It is a logical continuation of our previous benchmark of the protocol for the atomic case of RAES of the neon 1s −1 3p resonance, where it was shown to yield spectra and total decay rates in good agreement with experimental references. 55 The central approximation in the protocol is that the angular structure of the molecular potential is averaged out, leading to spherically symmetric continuum orbitals that are obtained by numerically solving the radial Schrödinger equation. As has been shown here, such an approach, being natural for atoms, in fact provides a valuable insight into the nature of molecular photoionization and autoionization spectral features as well.…”

“…In this section, we briefly present theory behind our method; the detailed description can be found in our recent article. 55 Atomic units (a.u.) are employed throughout this article, if not stated otherwise.…”

“…The article is organized as follows. First, we briefly recapitulate the theory behind our approach in Section II, which is presented in detail elsewhere, 55 and give the details of our computational setup in Section III. The X-ray Absorption Spectrum (XAS), RAES, and valence PES are discussed on a case to case basis for each molecule separately in Section IV.…”

Solvation and speciation of cobalt(II). A theoretical X-ray absorption and RIXS study

“…While K-edges are well described using timedependent density functional theory [16], the multiconfiguration and strong spin-orbit coupling (SOC) effects pertinent to transition metal L-edges make correlated wave function approaches the method of choice. Recently, a theoretical protocol based on the RASSCF method [17] has been successfully applied to studies of XAS [9,18], RIXS [5,6,12,19], partial fluorescence yield [10,13], photoelectron [20][21][22], and Auger [23] spectra, for a review see Ref. [2].…”

Feshbach-Fano Approach for Calculation of Auger Decay Rates Using Equation-of-Motion Coupled-Cluster Wave Functions: Numerical Examples and Benchmarks

“…As was shown in the Ref. [79], due to a local nature of the Auger process, the higher angular momentum of the emitted electron is, the less important the potential from the remaining core state is. This observation is confirmed by our calculations: for the d−wave Auger electrons the plane wave performs as good as the Coulomb wave.…”