Complex energy bands inα-brass

The average-$t$-matrix approximation (ATA) is used to evaluate complex energy bands in the disordered alloy $\alpha$-CuZn over a range of Zn concentrations between 0 and 30 at.%. The calculations are based on the Korringa-Kohn-Rostoker equations of band theory and on the use of atomic phase shifts obtained from renormalized-atom muffin-tin potentials. We examine the effects of charge transfer between the atomic constituents on the basis of two empirical models. Both models involve a single free parameter whose value is adjusted to guarantee agreement with the experimental shift in the optical-absorption edge as a function of Zn concentration. The effects of lattice expansion in $\alpha$-brass are also included and are shown to have a significant effect on the energies of various states the vicinity of the Fermi level. The present calculations are compared with the available experimental results on $\alpha$-brass. Good agreement is found with experiments sensitive to the real parts of the energy bands, for example, the concentration dependence of both the splitting of the 5-eV peak in the optical-absorption spectrum and the neck radii as determined by some of the positron-annihilation investigations. The theory agrees only qualitatively with the results of measurements sensitive to the imaginary parts of the bands such as Dingle temperatures and residual resistivities.