A cluster plus effective medium tight-binding study of SiOx systems

The valence band density of states of SiO_x amorphous systems is calculated using a tight-binding treatment. The Green's function method is applied to a small cluster embeddied in a suitable effective medium. An average of this Green's function is then performed assuming a statistical distribution of composition for the small clusters. The effective medium is treated as a Bethe lattice of the correct composition. The results are completely consistent with experiment if the Si O Si angle is assumed to decrease with x.