The perturbation of the surface density of electronic states by point defect – the connection with the topology of the isoenergetic curve

The discrete Schrodinger equation on two-dimensional Bravais lattice perturbed by a point potential is considered. The asymptotic behavior of the perturbation of the surface density of states is analyzed. It is established that the behavior of this perturbation depends mainly on the topological properties of the isoenergetic curve on the Brillouin zone.