Resonance study: Effect of partial triples excitation using complex absorbing potential‐based Fock‐space multi‐reference coupled cluster

Abstract

Resonances are metastable states with finite lifetime. They play important role in physics, chemistry and biology. The theoretical calculation of resonance state is a challenging problem. In this paper we have studied the shape resonance of Be, Mg, N 2 and CO. We have used correlated independent particle approximation to the Fock space multi-reference coupled cluster singles-doubles with third-order triples (CAP-CIP-FSMRCCSD(T)) method augmented by complex absorption potential. The resonance energy and decay widths are obtained by solving a non-Hermitian eigen-value problem within FSMRCC framework. The effects of the lowest order triples on the resonance energy and decay are studied.

Use of bound state methods to calculate partial and total widths of shape resonances

“…For the well-studied 2 P g valence anion of N 2 , bound state 16,17,20,29,[32][33][34] and scattering calculations carried out with high level treatment of electron correlation 14 have been found to give similar resonance parameters. Yet, as will be discussed below, this is not necessarily the case for the resonance widths for heteronuclear diatomic molecules or large organic molecules such as anthracene for which multiple partial waves contribute to the various TA resonances.…”

“…9 As such there is considerable interest in developing robust computational methodologies to model electron capture and detachment. 10–34…”

Selected Configuration Interaction for Resonances

“…In particular, CAP is one of the most widely used techniques for studying resonances. It has been combined with equation-of-motion electron-attached coupled-cluster with singles and doubles (EOM-EA-CCSD), 27,28,33 Fock-space multireference coupled-cluster, 34,35 turbative triples, 36,37 algebraic diagrammatic construction, 38−40 symmetry-adapted-cluster configuration interaction, 41 extended multiconfigurational quasidegenarate perturbation theory of the second order, 42,43 multireference configuration interaction, 26,44 and density-functional theory. 45 Despite significant theoretical advances in recent years, 10,11 the most accurate existing methods for molecular resonances cannot rival the level of accuracy that has been achieved for bound states.…”