title: Consequences of electron correlation for XPS binding energies: Representative case for C(1s) and O(1s) XPS of CO.
abstract: In this paper, we present a study of the signs and the magnitudes of the errors of theoretical binding energies, BE's, of the C(1s) and O(1s) core-levels compared to BE's measured in X-Ray photoemission, XPS, experiments. In particular, we explain the unexpected sign of the error of the Hartree-Fock C(1s) BE, which is larger than experiment, in terms of correlation effects due to the near degeneracy of the CO(1π) and CO(2π) levels and show how taking this correlation into account leads to rather accurate predicted BE's. We separate the initial state contributions of this near degeneracy, present for the ground state wavefunction, from the final state near degeneracy effects, present for the hole state wavefunctions. Thus, we are able to establish the importance for the core-level BE's of initial state charge redistribution due to the π near-degeneracy. While the results for CO are interesting in their own right, we also consider whether our conclusions for CO are relevant for the analysis of XPS spectra of a wider range of molecules.
authors: Department of Chemistry, University of North Texas, Denton, Texas 76203-5017, USA.
authors: Paul S
authors: PS
authors: Bagus
authors: Departament de Ciència de Materials i Química Física and Institut de Química Teòrica i Computacional (IQTCUB), Universitat de Barcelona, C/Martí i Franquès 1, 08028 Barcelona, Spain.
authors: Carme
authors: C
authors: Sousa
authors: Departament de Ciència de Materials i Química Física and Institut de Química Teòrica i Computacional (IQTCUB), Universitat de Barcelona, C/Martí i Franquès 1, 08028 Barcelona, Spain.
authors: Francesc
authors: F
authors: Illas