The electronic properties of ${\text{LiCoO}}_2$ have been studied by theoretical band-structure calculations (using density functional theory) and experimental methods (photoemission). Synchrotron-induced photoelectron spectroscopy, resonant photoemission spectroscopy (ResPES), and soft x-ray absorption (XAS) have been applied to investigate the electronic structure of both occupied and unoccupied states. High-quality PES spectra were obtained from stoichiometric and highly crystalline ${\text{LiCoO}}_2$ thin films deposited “in situ” by rf magnetron sputtering. An experimental approach of separating oxygen- and cobalt-derived (final) states by ResPES in the valence-band region is presented. The procedure takes advantage of an antiresonant behavior of cobalt-derived states at the $3p\text{−}3d$ excitation threshold. Information about the unoccupied density of states has been obtained by $\text{O}K$ XAS. The structure of the $\text{Co}L$ absorption edge is compared to semiempirical charge-transfer multiplet calculations. The experimental results are furthermore compared with band-structure calculations considering three different exchange potentials [generalized gradient approximation (GGA), using a nonlocal Hubbard $U$ $\left(\text{GGA}+U\right)$ and using a hybrid functional (Becke, three-parameter, Lee-Yang-Parr [B3LYP])]. For these different approaches total density of states and partial valence-band density of states have been investigated. The best qualitative agreement with experimental results has been obtained by using a $\text{GGA}+U$ functional with $U=2.9\text{eV}$.

• Received 6 December 2009

DOI:https://doi.org/10.1103/PhysRevB.82.195431