Bethe-Salpeter Equation Calculations of Core Excitation Spectra

TL;DR

This paper introduces a hybrid computational approach combining GW/BSE methods with ab initio wavefunctions and PAW transition matrix elements to accurately simulate core excitation spectra such as XAS, EELS, and NRIXS.

Contribution

It develops and implements the OCEAN interface for efficient core excitation calculations using a combination of ab initio codes and many-pole GW models, including multiplet effects.

Findings

Accurate simulation of K-edges in LiF and KCl

Successful modeling of Ti L2,3-edge in SrTiO3

Effective reproduction of experimental spectra

Abstract

We present a hybrid approach for GW/Bethe-Salpeter Equation (BSE) calculations of core excitation spectra, including x-ray absorption (XAS), electron energy loss spectra (EELS), and non-resonant inelastic x-ray scattering (NRIXS). The method is based on {\it ab initio} wavefunctions from the plane-wave pseudopotential code ABINIT; atomic core-level states and projector augmented wave (PAW) transition matrix elements; the NIST core-level BSE solver; and a many-pole GW self-energy model to account for final-state broadening and self-energy shifts. Multiplet effects are also accounted for. The approach is implemented using an interface dubbed OCEAN (Obtaining Core Excitations using ABINIT and NBSE). To demonstrate the utility of the code we present results for the K-edges in LiF as probed by XAS and NRIXS, the K-edges of KCl as probed by XAS, the Ti L_2,3-edge in SrTiO_3 as probed by XAS, and the Mg L_2,3-edge in MgO as probed by XAS. We compare the results to experiments and results obtained using other theoretical approaches.