THE ELECTRONIC-STRUCTURE OF LA2CUO4

The electronic structure of the strongly correlated system La2CuO4 is calculated, using a realistic tight-binding model for the electronic s tates in the Copper Oxide planes. The model includes the Oxygen p (x) and p (y) orbitals and the Copper 3 d (x2-y2) orbitals. The hybridizat ion between the Copper d (x2-y2) and the Oxygen p (x) and p (y) orbita ls is considered, as well as the direct overlap between the p orbitals of neighboring Oxygen ions. The Coulomb interaction between the elect rons in the d shell of the Copper ions is treated by introducing slave bosons, thereby restricting the allowed Cu ionic configurations in th e system to be Cu++ and Cu+. The system may exhibit a phase characteri zed by the participation of the d electrons in coherent itinerant stat es. However, there also exists the possibility of another phase charac terized by the localization of the d electrons. This second phase occu rs when the bare charge transfer energy is sufficiently large. Thus, f or the stochiometric system them are two possible zero temperature sta tes; a metallic state and a charge transfer insulator state. The p-p h opping matrix element is large and it is found that its sip, relative to the other hopping matrix elements, has a significant effect on the position of the phase boundary. Inferring values tight-binding integra ls from band structure calculations, one concludes that the paramagnet ic phase Of La2CuO4 should be metallic. The electronic structure and F ermi-surface are calculated for this phase. The presence of long range d anti-ferromagnetic order is expected to open up a Slater pp at the F ermi-energy, yielding the experimentally observed low temperature insu lating phase.