Feshbach-Dyson method for calculations of Auger decay rates

Photon absorption in the X-ray domain generally leads to creation of highly excited species with core-electron vacancies. One of the major relaxation channels for such states is Auger decay - a process accompanied by spontaneous emission of free electron(s). While Auger decay in atoms and molecules has been known for long now, its predictive modeling still poses a significant challenge for theorists, as it intrinsically involves electronic continuum and many-body electronic states which are formally unbound (metastable).
Here we present a novel approach to calculate Auger decay rates and spectra based on Fano-Feshbach resonance theory and equation-of-motion coupled-cluster method (EOM-CCSD). We apply core-valence separation (CVS) technique and appropriate EOM models to obtain the correct (both initial and final) electronic states that occur in the Auger decay. Then, all Auger partial rates and energy corrections are computed via contraction of two-body Dyson functions (an equivalent of two-particle transition density matrix) with proper two-electron integrals involving a free electron orbital. Results of our benchmark calculations for atomic and molecular systems demonstrate that the presented method yields highly robust and accurate Auger parameters.