Core ionization energies (IE) are accurately estimated using ΔSCF and Slater's transition state (STS). The small remaining errors come mainly from self-interaction error and can be corrected with the “shifted STS (1)” and “shifted STS (2)” methods, thus providing a convenient means for predicting core IE.

Abstract

The core ionization energies of second- and third-period elements of the molecules C₂H₅NO₂, SiF₄, Si(CH₃)₄, PF₃, POF₃, PSF₃, CS₂, OCS, SO₂, SO₂F₂, CH₃Cl, CFCl₃, SF₅Cl, and Cl₃PS are calculated by using Hartree-Fock (HF), and Kohn-Sham (KS) with BH&HLYP, B3LYP, and LC-BOP functionals. We used ΔSCF, Slater's transition state (STS), and two previously proposed shifted STS (1) and shifted STS (2) methods, which have been developed. The errors of ΔSCF and STS come mainly from the self-interaction errors (SIE) and can be corrected with a shifting scheme. In this study, we used the shifting parameters determined for each atom. The shifted STS (1) reproduces ΔSCF almost perfectly with mean absolute deviations (MAD) of 0.02 eV. While ΔSCF and STS vary significantly depending on the functional used, the variation of shifted STS (2) is small, and all shifted STS (2) values are close to the observed ones. The deviations of the shifted STS (2) from the experiment are 0.24 eV (BH&HLYP), 0.19 eV (B3LYP), and 0.23 eV (LC-BOP). These results further support the use of shifted STS methods for predicting the core ionization energies.