Quasiparticle energy spectra of isolated atoms from coupled-cluster singles and doubles (CCSD): Comparison with exact CI calculations

TL;DR

This paper demonstrates that the GFCCSD method accurately reproduces quasiparticle spectra, including satellite peaks and Mott gaps, for isolated atoms, aligning well with exact CI calculations and surpassing DFT in certain aspects.

Contribution

The study shows that GFCCSD can reliably calculate atomic energy spectra, capturing satellite features and Mott gaps, offering a new tool for detailed electronic state analysis.

Findings

GFCCSD reproduces quasiparticle and satellite peaks accurately.

GFCCSD captures Mott gaps in open-shell atoms.

Satellite peaks originate from shake-up effects.

Abstract

In this study, we have calculated single-electron energy spectra via the Green's function based on the coupled-cluster singles and doubles (GFCCSD) method for isolated atoms from H to Ne. In order to check the accuracy of the GFCCSD method, we compared the results with the exact ones calculated from the full-configuration interaction (FCI). Consequently, we have found that the GFCCSD method reproduces not only the correct quasiparticle peaks but also satellite ones by comparing the exact spectra with the 6-31G basis set. It is also found that open-shell atoms such as C atom exhibit Mott gaps at the Fermi level, which the exact density-functional theory (DFT) fails to describe. The GFCCSD successfully reproduces the Mott HOMO-LUMO (highest-occupied molecular orbital and lowest-unoccupied molecular orbital) gaps even quantitatively. We also discussed the origin of satellite peaks as shake-up effects by checking the components of wave function of the satellite peaks. The GFCCSD is a novel cutting edge to investigate the electronic states in detail.