Angular dependence of core hole screening inLiCoO2: ADFT+Ucalculation of the oxygen and cobaltK-edge x-ray absorption spectra

Abstract

Angular-dependent core hole screening effects have been found in the cobalt $K$-edge x-ray absorption spectrum of ${\text{LiCoO}}_{2}$, using high-resolution data and parameter-free general gradient approximation plus $U$ calculations. The $\text{Co}\text{ }1s$ core hole on the absorber causes strong local attraction. The core hole screening on the cobalt nearest-neighbors induces a 2 eV shift in the density of states with respect to the on-site $1s\text{\ensuremath{-}}3d$ transitions, as detected in the $\text{Co}\text{ }K$ pre-edge spectrum. Our density functional theory plus $U$ 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.