Ab initio multiplet plus cumulant approach for correlation effects in x-ray photoelectron spectroscopy

TL;DR

This paper introduces a combined ab initio multiplet and cumulant approach to accurately model correlation effects in x-ray photoelectron spectroscopy, capturing both atomic multiplets and satellite features.

Contribution

It presents a novel method that separates local and long-range Coulomb interactions to improve the modeling of correlation effects in XPS.

Findings

Successfully explains multiplet peaks in transition metal oxides

Reproduces charge-transfer satellites observed in experiments

Accounts for distributed background features in XPS spectra

Abstract

The treatment of electronic correlations in open-shell systems is among the most challenging problems of condensed matter theory. Current approximations are only partly successful. Ligand field multiplet theory (LFMT) has been widely successful in describing intra-atomic correlation effects in x-ray spectra, but typically ignores itinerant states. The cumulant expansion for the one electron Greens function has been successful in describing shake-up effects but ignores atomic multiplets. More complete methods, such as dynamic mean-field theory can be computationally problematic. Here we show that separating the dynamic Coulomb interactions into local and longer-range parts with ab initio parameters yields a combined multiplet plus cumulant approach that accounts for both local atomic multiplets and satellite excitations. The approach is illustrated in transition metal oxides and explains the multiplet peaks, charge-transfer satellites and distributed background features observed in XPS experiment.