  We propose a many-body method for band-structure calculations in strongly
correlated electron systems and apply it to NiO. The method may be viewed as a
translationally invariant version of the cluster method of Fujimori and Minami.
Thereby the Coulomb interaction within the d-shells is treated by exact
diagonalization and the d-shells then are coupled to a solid by an extension of
the cluster perturbation theory due to Senechal et al. The method is
computationally no more demanding than a conventional band structure
calculation and for NiO we find good agreement between the calculated single
particle spectral function and the experimentally measured band structure.
