Feshbach-Fano Approach for Calculation of Auger Decay Rates Using Equation-of-Motion Coupled-Cluster Wave Functions: Theory and Implementation

Abstract

<p>We present a novel methodology to calculate Auger decay rates based on equation-of -motion coupled-cluster singles and doubles (EOM-CCSD) wave function, combined with a simplified continuum orbital describing the outgoing electron. In our approach the Auger process is considered as an autoionization of a resonant electronic state, which can be described with Feshbach-Fano projection technique in order to distill the resonance parameters. To this end, we employ core-valence separation (CVS) scheme as a method to extract the bound part of the decaying many-electronic state. Main advantages of our methodology include (1) flexible EOM-CCSD ansatz enabling to describe various electronic states, (2) simple, yet universal computational setup, (3) fast computations due to fully analytical evaluation of all mixed bound-continuum two-electron integrals, and (4) implementation in general-purpose software package for quantum-chemical calculations.</p>

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

“…We have presented numeric results illustrating the performance of the extension of the EOM-CCSD formalism [26] to the computation of Auger decay rates in atoms and molecules. We calculated Auger decay rates using the Feshbach-Fano formalism, with manyelectron EOM-CC states and a continuum orbital describing the outgoing electron approximated by either a plane wave or a Coulomb wave.…”

“…Here, we test two simple approaches for the continuum orbital: a plane wave, and a Coulomb wave expanded in terms of auxiliary basis set of the products of Gaussian and plane wave functions (GPW). The details of the implementation of mixed GTO-GPW integrals are described in the companion paper [26]. As for the Coulomb wave, the expansion coefficients in terms of the GPW functions were generated following the pseudo-partial wave method of Szczygie l et al [31].…”

“…The lifetimes of the core-level states and the respective broadening of the spectral lines could not be computed. In our companion paper [26], we presented the extension of the theory to compute the decay rates of the core-level states.…”

“…1, Auger decay is a process in which an Nelectron highly excited core-level state decays into an N -1 electron valence state and a free electron. The theoretical framework, described in the companion paper [26], is based on the Feshbach-Fano treatment of resonance phenomena. In this approach, the full function space is artificially divided into the bound and unbound spaces, and the resonances are described in terms of the interacting diabatic-like states, representing the bound part of the resonance and the continuum decay channels, respectively.…”

Molecular-Orbital Framework of Two-Electron Processes: Application to Auger and Intermolecular Coulomb Decay.

“…2). Mathematically, it means that this transition requires three creation/annihilation operators, giving rise to two-body Dyson orbitals [34][35][36][37] :…”