The theory of disordered alloys. III. Cluster theory and off-diagonal disorder

For pt.II see ibid., vol.4, p.1351 (1974). A cluster theory method based on a continued fraction expansion of the Green function has been used to calculate the density of states of a model simple cubic alloy with both diagonal and off-diagonal disorder. For a particular form of off-diagonal disorder the calculation reduces to a simple modification of a cluster theory method presented earlier by Jacobs. For a more general form of off-diagonal disorder the calculation is harder to carry out but results are nevertheless presented. The results show a density of states with a great deal of structure which may be expected to reproduce many more moments correctly than the best previous theory which reproduces only four moments correctly.