Juhan Matthias Kahk

The ‐self‐consistent‐field (SCF) method permits calculations of core electron binding energies in materials and molecules at a modest computational cost. However, it has been reported that whilst this method works well for small molecules, its accuracy drops off dramatically when larger systems are considered. Particularly large errors have been reported for the anthrone molecule, which consists of 25 atoms. In this work, the gas‐phase photoelectron spectrum of anthrone is revisited both computationally and experimentally. The measured C 1s binding energies in anthrone differ markedly from previously published values, and the new experimental results are in good agreement with SCF calculations. In addition, the performance of the SCF method is evaluated for a dataset of 44 core electron binding energies from medium‐sized molecules containing between 10 and 40 atoms. Both SCAN and B3LYP yield a mean absolute error of 0.19 eV for this dataset. This level of accuracy is comparable to the results of previous computational benchmarks. Overall, these results and general theoretical considerations indicate that the SCF method is suitable for modelling localized excitations in both small and large molecules, and applications to other extended systems are also promising.

An investigation of the electronic structure of K ₂ SiF ₆ based on GW theory and photoelectron spectroscopy reveals that Auger–Meitner decay of K 3p holes is energetically forbidden in this material.

For the computational prediction of core electron binding energies in solids, two distinct kinds of modeling strategies have been pursued: the Δ-Self-Consistent-Field method based on density functional theory (DFT), and the GW method. In this study, we examine the formal relationship between these two approaches and establish a link between them. The link arises from the equivalence, in DFT, between the total energy difference result for the first ionization energy, and the eigenvalue of the highest occupied state, in the limit of infinite supercell size. This link allows us to introduce a new formalism, which highlights how in DFT─even if the total energy difference method is used to calculate core electron binding energies─the accuracy of the results still implicitly depends on the accuracy of the eigenvalue at the valence band maximum in insulators, or at the Fermi level in metals. We examine whether incorporating a quasiparticle correction for this eigenvalue from GW theory improves the accuracy of the calculated core electron binding energies, and find that the inclusion of vertex corrections is required for achieving quantitative agreement with experiment.

Spectroscopies that probe electronic excitations from core levels into unoccupied orbitals, such as X-ray absorption spectroscopy and electron energy loss spectroscopy, are widely used to gain insight into the electronic and chemical structure of materials. To support the interpretation of experimental spectra, we assess the performance of a first-principles approach that combines linear-response time-dependent density (TDDFT) functional theory with the Δ self-consistent field (ΔSCF) approach. In particular, we first use TDDFT to calculate the core-level spectrum and then shift the spectrum such that the lowest excitation energy from TDDFT agrees with that from ΔSCF. We apply this method to several small molecules and find encouraging agreement between calculated and measured spectra.

We have used the ΔSCF method for calculating TM 2p _3/2 core electron binding energies in compounds of first row transition metals. After correcting for element dependent systematic errors, the MAE of the calculated binding energies is just 0.20 eV.