The role of Zhang-Rice singlet-like excitations in one-dimensional   cuprates
  We present the first calculation of the electron-energy loss spectrum of infinite one-dimensional undoped CuO_3 chains within a multi-band Hubbard model. The results show good agreement with experimental spectra of Sr_2CuO_3. The main feature in the spectra is found to be due to the formation of Zhang-Rice singlet-like excitations. The q-dependence of these excitations is a consequence of the inner structure of the Zhang-Rice singlet. This makes the inclusion of the oxygen degrees of freedom essential for the description of the relevant excitations. We observe that no enhanced intersite Coulomb repulsion is necessary to explain the experimental data. 
J. Richter, C. Waidacher, K. W. Becker