CORRELATION AND DISORDER EFFECTS IN PHOTOELECTRON AND AUGER-SPECTRA -THE LATE TRANSITION-METALS AND THEIR ALLOYS

We consider the case of narrow, almost filled valence-band solids and present a method for an nb initio description of correlation and disor der effects in the one-particle spectrum as seen in photoemission. For filled (empty) bands, we also consider the two-body propagator, which enters the theoretical formulation of Auger emission. In order to dea l with the late transition metals and their alloys: (i) we consider th e case of an almost filled band, homogeneous solid, with band degenera cy, Coulomb and spin-orbit interactions; after deriving a k-dependent self-energy in the T-matrix approximation, we recover its local, nondi spersive limit, to be used in the nonhomogeneous case;and (ii) for the case of substitutional disorder, we introduce a minimal-size supercel l approach in which correlation effects are treated by a local self-en ergy as calculated in (i) and disorder is included by a constrained de termination of the supercell configuration. The method and its signifi cance for realistic nb initio calculations of correlated, disordered a lloys are illustrated in terms of a single band, disordered-Hubbard Ha miltonian. Model results for the one- and two-body spectra are shown a nd discussed.