Selected Configuration Interaction for Resonances

TL;DR

This paper introduces CAP-SCI, a novel method combining selected configuration interaction with complex absorbing potentials to accurately compute electronic resonance positions and widths, surpassing previous models in precision.

Contribution

The paper develops CAP-SCI, a new approach that extends selected configuration interaction to resonances using CAP, achieving high-accuracy results for resonance properties.

Findings

CAP-SCI accurately predicts resonance positions and widths.

High-order correlation significantly affects resonance calculations.

CAP-SCI outperforms previous methods like EOM-CCSD in accuracy.

Abstract

Electronic resonances are metastable states that can decay by electron loss. They are ubiquitous across various fields of science, such as chemistry, physics, and biology. However, current theoretical and computational models for resonances cannot yet rival the level of accuracy achieved by bound-state methodologies. Here, we generalize selected configuration interaction (SCI) to treat resonances using the complex absorbing potential (CAP) technique. By modifying the selection procedure and the extrapolation protocol of standard SCI, the resulting CAP-SCI method yields resonance positions and widths of full configuration interaction quality. Initial results for the shape resonances of \ce{N2-} and \ce{CO-} reveal the important effect of high-order correlation, which shifts the values obtained with CAP-augmented equation-of-motion coupled-cluster with singles and doubles by more than \SI{0.1}{\eV}. The present CAP-SCI approach represents a cornerstone in the development of highly-accurate methodologies for resonances.