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We have extended the single-impurity cluster model to include the efFects of charge transfer to the conduction band. It is found that these efFects can have a considerable inAuence on the line shapes of core-level spectra of small-gap transition-metal compounds. Using a few additional, well-defined parameters to describe the interactions between the local cluster and the conduction band, and retaining the original intracluster parameters from previous single-impurity models, we find an improved agreement for the Ni 2p spectrum of NiS. The asymmetric line shape is well reproduced, keeping the correct satellite to main peak ratio, which is not possible using the three-peak structure of previous models. The new model is less successful in explaining efFects beyond standard single-impurity models in more ionic compounds, such as the double-peak stucture of the main line of the core-level spectrum of NiQ, where the interactions between the metal d site and the conduction band are expected to play a lesser role.

The electronic structures of the itinerant ferromagnets Cr 1Ϫ␦ Te (␦ϭ0.05, 0.25, and 0.375͒ have been studied by photoemission spectroscopy. The valence-band spectra are compared with the density of states given by band-structure calculations. In spite of the itinerant nature of the d electrons, disagreement between the photoemission spectra and the band-structure calculations exists in the magnitude of the d-band exchange splitting and the spectral weight at the Fermi level and 2-4 eV below it: The occupied d band for ␦ϭ0.05 is shifted away from the Fermi level; the observed spectral weight at the Fermi level is significantly suppressed compared with the band-structure calculations for ␦ϭ0.05 and 0.375, where the nominal d-electron numbers are close to integers 4 and 3, respectively. Configuration-interaction cluster-model calculations have been made for ␦ϭ0.05 and 0.375 to explain the spectral weight distribution in the high-binding-energy ͑2-4 eV͒ region in terms of electron-correlation effects. The d-d on-site Coulomb energy is estimated to be significant, Uϳ2 eV, and nearly equal to or smaller than the charge-transfer energy ⌬ϳ2 -3 eV.

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