Abstract (by Editor) A detailed report is given of the theoretical work carried out by the author during recent years on problems connected with the energy spectrum of a disordered solid. The treatment is general, with indications of applications to particular problems, such as the lattice vibrational spectrum of an imperfect crystal and the electronic levels associated with impurity atoms. Particular attention is given to the behaviour of the density of states (spectral density) of both the levels derived from those of the perfect crystal and the impurity levels. The effects of ordering of imperfections is considered, and some discussion of other approximations and models is given.
I.M. Lifshitz (Thu,) studied this question.