Strong nonlocal contributions to Cu 2pphotoelectron spectroscopy

Calculations of Cu 2p photoelectron spectra for a Cu₃{O}₁₀$ cluster with a reduced basis set show that the introduction of more Cu sites leads to a revised interpretation of the Cu 2p spectrum. Besides the usual peaks of mainly 3${d}⁹$ and 3${d}¹⁰$L character another peak appears at lower binding energy. This peak is of mainly 3${d}¹⁰$ character. The hole has moved away from the core hole potential and has formed a Zhang-Rice singlet on a neighboring ${CuO}₄$ unit. This effect explains the asymmetric line shape of the main line in the Cu 2p spectra of CuO and the high-${T}c$ compounds. For formally trivalent copper compounds, such as ${NaCuO}₂$, this effect disappears and a narrow line shape is observed. The consequences of hole doping (33%) on the Cu 2p spectra have also been studied. The peak assignment turns out to be very similar to that of the undoped system.