Reference Energies for Valence Ionizations and Satellite Transitions

Upon ionization of an atom or a molecule, another electron
(or
more) can be simultaneously excited. These concurrently generated
states are called “satellites” (or shakeup transitions)
as they appear in ionization spectra as higher-energy peaks with weaker
intensity and larger width than the main peaks associated with single-particle
ionizations. Satellites, which correspond to electronically excited
states of the cationic species, are notoriously challenging to model
using conventional single-reference methods due to their high excitation
degree compared to the neutral reference state. This work reports
42 satellite transition energies and 58 valence ionization potentials
(IPs) of full configuration interaction quality computed in small
molecular systems. Following the protocol developed for the quest database [Véril, M.; Scemama, A.; Caffarel, M.; Lipparini,
F.; Boggio-Pasqua, M.; Jacquemin, D.; and Loos, P.-F. Wiley Interdiscip.
Rev.: Comput. Mol. Sci. 2021, 11, e1517],
these reference energies are computed using the configuration interaction
using a perturbative selection made iteratively (CIPSI) method. In
addition, the accuracy of the well-known coupled-cluster (CC) hierarchy
(CC2, CCSD, CC3, CCSDT, CC4, and CCSDTQ) is gauged against these new
accurate references. The performances of various approximations based
on many-body Green’s functions (GW, GF2, and T-matrix) for IPs are also analyzed. Their limitations in
correctly modeling satellite transitions are discussed.