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