Second order Møller-Plesset and coupled cluster singles and doubles methods with complex basis functions for resonances in electron-molecule scattering

Abstract

The method of complex basis functions is applied to molecular resonances at correlated levels of theory. Møller-Plesset perturbation theory at second order and equation-of-motion electron attachment coupled-cluster singles and doubles (EOM-EA-CCSD) methods based on a non-Hermitian self-consistent-field reference are used to compute accurate Siegert energies for shape resonances in small molecules including N, CO, CO, and CHO. Analytic continuation of complex 𝜃-trajectories is used to compute Siegert energies, and the 𝜃-trajectories of energy differences are found to yield more consistent results than those of total energies. The ability of such methods to accurately compute complex potential energy surfaces is investigated, and the possibility of using EOM-EA-CCSD for Feshbach resonances is explored in the context of e-helium scattering.

Elektronische Resonanzzustände – warum die Energie komplex sein kann, Trendbericht Theoretische Chemie 2020, Teil 1

“…Dies trifft beispielsweise auf Equation-of-Motion-Coupled-Cluster(EOM-CC)-Methoden zu, die mit CAPs, [17][18][19][20] komplexer Skalierung 21) und komplexen Basisfunktionen 22,23) kombiniert wurden. Eng verwandt sind symmetrieadaptierte Konfigurationswechselwirkungs(SAC-CI)-Methoden, auch sie wurden mit CAPs kombiniert.…”

Calculation of the Lowest Resonant States of H− and Li by the Complex Absorbing Potential Method

“…The resonance widths are estimated in the range 0.38-0.63 eV [31][32][33]43,47,55] at the experimental value of 0.4 eV. The maximum theoretical value of the resonance width (1.3 eV) was obtained in [43]. The sensitivity can explain the error of theoretical results to a quality of the basis of atomic orbitals (AO) and parameters of the absorbing potential [32,33].…”

“…For the lowest resonance CO − ( 2 Π) at an equilibrium internuclear distance, the energy estimates are in the range 1.90-2.08 eV [31][32][33]43,47,55] and exceed the experimental value of 1.50 eV [56]. The resonance widths are estimated in the range 0.38-0.63 eV [31][32][33]43,47,55] at the experimental value of 0.4 eV. The maximum theoretical value of the resonance width (1.3 eV) was obtained in [43].…”

Fitting continuum wavefunctions with complex Gaussians: Computation of ionization cross sections

“…Complex Gaussians have already been proven to be successful in resonance stabilization calculations, where they arise from a complex scaling transformation. [27][28][29][30] Such functions possess an intrinsically oscillatory behavior that may facilitate the task of representing continuum states over larger radial domains. Previous investigation in this line, include the work of Matsuzaki et al who used complex Slater orbitals [31] and complex Gaussians [32] in photoionization calculations.…”