Fine Structure of Electronic Spectra of Binary Substitutional Alloys in a Single‐Band Model

The fine structure of the electronic density of states due to clusters of impurity atoms in disordered binary alloys is studied for a single‐band model with a short‐range random scattering potential. The sum of the n ‐centre contributions to the total T ‐matrix is obtained for n = 1, 2, 3. The T ‐matrix describes the scattering corrections to an optimum one‐centre approximation which is determined self‐consistently in each case. For n = 1, the method is identical with the coherent potential approximation (CPA). Comparison of the results for n = 1 and n = 2 gives a criterion for validity of the CPA. A simple one‐dimensional model is studied numerically in the two‐centre approximation and the results are compared with the CPA and the direct solution for a finite chain.