Angular dependence of core hole screening in LiCoO2: A DFT+U calculation of the oxygen and cobalt K-edge x-ray absorption spectra

TL;DR

This study uses DFT+U calculations to analyze how core-hole screening in LiCoO2 varies with angle, revealing significant off-site effects and the importance of the core-hole and Hubbard U in spectral features.

Contribution

It provides a detailed theoretical analysis of angular dependent core-hole screening effects in LiCoO2's x-ray absorption spectra using parameter-free GGA+U calculations.

Findings

Core-hole screening causes energy shifts in spectra.

Off-site screening varies with direction, affecting spectral features.

U parameter improves the description of screening effects.

Abstract

Angular dependent core-hole screening effects have been found in the cobalt K-edge x-ray absorption spectrum of LiCoO2, using high-resolution data and parameter-free GGA+U calculations. The Co 1s core-hole on the absorber causes strong local attraction. The core-hole screening on the nearest neighbours cobalt induces a 2 eV shift in the density of states with respect to the on-site 1s-3d transitions, as detected in the Co K pre-edge spectrum. Our DFT+U calculations reveal that the off-site screening is different in the out-of-plane direction, where a 3 eV shift is visible in both calculations and experiment. The detailed analysis of the inclusion of the core-hole potential and the Hubbard parameter U shows that the core-hole is essential for the off-site screening, while U improves the description of the angular dependent screening effects. In the case of oxygen K-edge, both the core-hole potential and the Hubbard parameter improve the relative positions of the spectral features.