Electronic structure ofNaCuO2

We analyze the experimental core-level photoemission and x-ray absorption (XA) spectra of ${\mathrm{NaCuO}}_2$ in terms of an Anderson-impurity Hamiltonian including the band-structure effects of the oxygen sublattice and show that the XA results unambiguously indicate a negative value of the charge-transfer energy Δ. We also perform mean-field calculations for the electronic structure for the edge-shared one-dimensional ${\mathrm{CuO}}_2$ lattice of ${\mathrm{NaCuO}}_2$ within the multiband Hubbard Hamiltonian and show that the origin of the insulating nature lies in band-structure rather than correlation effects, and that the gap has a pd-p character.