An investigation of the momentum dependence of the electronic spectrum fora disordered system

The spectral properties of disordered systems are investigated using two-di mensional examples in the tight-binding approximation. The spectra are exam ined as functions of the momentum wavevector for two-dimensional systems. A particular example is the directional dependence of the spectrum for a qua sicrystal, represented by a two-dimensional Penrose lattice. The spectrum c hanges dramatically, as expected, when the momentum vector moves off a symm etry axis of the system. The value of this approach for analysing the elect ronic properties of structurally disordered systems is discussed.