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We calculate the direct and inverse photoemission spectra of 3d transition metals with fcc or bcc structure. The dynamics of the d electrons is described by an extended Hubbard model including five canonical d bands in the one-particle operator Ho and all relevant on-site Coulomb and exchange matrix elements in the interaction Hamiltonian Hz. For the ground state a quantum-chemical ansatz is made taking local spin and density correlations into account. The retarded Green's functions of the d electrons are evaluated by using the projection technique of Mori and Zwanzig. Thereby the dynamics of the additional particle is projected onto local spin and density excitations in analogy to the ground-state calculation and treated exactly within that restricted operator space. In the case of Ni the correct satellite position and a reasonable reduction factor of the bandwidth are obtained by using an experimentally determined parameter set. The numerical calculations for our model Hamiltonian also predict multiplet structures in the photoemission spectra of Co and Fe.

We calculate the single-particle excitation spectrum of holes in the Emery model thereby extending and improving previous calculations. The system is considered at half filling (ni, = 1, one hole per Cu02 unit) and for hole doping, where the on-site hole-hole repulsions are kept finite. A paramagnetic form of the ground state is used. For the determination of the retarded Green's functions of copper and oxygen holes, the projection technique is applied solving the resulting equations of motions self-consistently. At half Ailing, the excitation spectrum exhibits a charge-transfer gap bounded by Zhang-Rice singlet states and the upper Hubbard band. Upon hole doping the Qat singlet band crosses the Fermi level giving rise to a large Fermi surface at a hole concentration of np, --1.25. Moreover, spectral weight is shifted from the upper Hubbard band to the states near the Fermi energy. The calculated spectral densities, the singlet dispersion for the doped system, and the transfer of spectral weight are in good quantitative agreement with exact diagonalization results for 2x2 Cu02 cluster.

We calculate the photoemission and inverse photoemission spectra of holes in copper-oxygen planes, the characteristic structural unit of high-temperature superconductors. The computations are based on the extended Hubbard or Emery model in the limit of infinitely strong Coulomb repulsion Ug on copper sites. In order to evaluate the corresponding one-particle correlation functions the projection technique is applied, which is especially suitable for strongly correlated systems.Thereby the hole dynamics is restricted to a subspace of relevant operators, within which it can be treated exactly. In contrast to independent-particle approximations the excitation spectra show Bn energy gap at half-filling, which disappears when the system is doped with additional holes. Besides the insulator-to-metal transition the strong correlations lead also to a significant shift of spectral weight to states close to the Fermi energy when the hole concentration increases. Our results are in good agreement with the ones of exact diagonalization studies of the (Cu02)4 cluster with periodic boundary conditions.