VALENCE STATES OF COPPER IONS AND ELECTRONIC-STRUCTURE OF LICU2O2

The electronic structure of LiCu2O2 was studied using x-ray emission ( Cu L-alpha, O K-alpha) and photoelectron spectroscopy (valence band an d core levels) as well as band-structure calculations in terms of loca l spin-density approximation (LSDA) and LSDA + U approaches. According to the x-ray-emission and photoelectron spectra the valence states of the Cu atoms are found to be mixed, i.e., 2+ and 1+. The LSDA calcula tions are contradictory to the experimental data and cannot reproduce the band gap and magnetic properties of LiCu2O2. The LSDA + U calculat ions describe the insulator and antiferromagnetic properties much bett er but the overestimation of the screened Coulomb parameter U leads to a binding-energy shift of the Cu-II 3d states and this distorts the p roper modeling of the valence-band structure. The magnetic structure o f LiCu2O2 is discussed, taking our LSDA + U band-structure calculation s into account. [S0163-1829(98)04108-3].