Analytical ground state for the three-band Hubbard model

For the calculation of charge excitations as those observed in, e.g., photo emission spectroscopy or in electron-energy-loss spectroscopy, a correct de scription of ground-state charge properties is essential. In strongly corre lated systems like the undoped cuprates this is a highly nontrivial problem . In this paper we derive a nonperturbative analytical approximation for th e ground state of the three-band Hubbard model on an infinite, half-filled CuO2 plane. By comparison with projector quantum Monte Carlo calculations i t is shown that the resulting expressions correctly describe the charge pro perties of the ground state. Relations to other approaches are discussed. T he analytical ground state preserves size consistency and can be generalize d for other geometries, while still being both easy to interpret and to eva luate. [S0163-1829(99)01628-8].