Channel-specific core-valence projectors for determining partial Auger decay widths

TL;DR

This paper introduces channel-specific core-valence projectors for calculating partial Auger decay widths, improving the analysis of core-ionized states in molecules using complex-variable coupled-cluster methods.

Contribution

The paper presents a novel technique called Auger channel projectors for evaluating partial decay widths in complex-variable electronic-structure calculations.

Findings

Channel-specific projectors enable accurate partial width calculations.

Combination of CIS calculations can recover CC decay widths effectively.

Method applied successfully to neon, water, ammonia, and methane.

Abstract

Auger decay is a relaxation process of core-vacant states in atoms and molecules, in which one valence electron fills the core vacancy while a second one is emitted. These states pose a challenge to electronic-structure theory, because they are embedded in the ionization continuum. Recently, we showed that molecular Auger decay can be described using complex-variable coupled-cluster (CC) methods and that partial widths and branching ratios can be computed based on a decomposition of the CC energy. Here, we introduce channel-specific core-valence projectors, dubbed Auger channel projectors, as a more general technique to evaluate partial widths from complex-variable treatments. We apply this new method to core-ionized states of neon, water, ammonia, and methane using CC singles and doubles (CCSD), equation-of-motion ionization potential CCSD, and configuration interaction singles (CIS) wave functions. Even though a single CIS calculation can never describe all Auger decay channels at once, we show that a combination of CIS calculations based on different reference states is able to recover partial and total decay widths from CC calculations to an excellent degree.