Eigenvalue problem of square and hexagon lattice

The purpose of using such tasks is called The tight-binding model. Because the task is low-dimensional, the energy structure of the electrons is assumed with the upcoming wave function compound obtained by the suppression of the wavelength functions of isolated atoms. The tight-binding model gives good results in many cases. And it can be easily combined with other models to get better results. Regardless the fact that this is a single electronic model it is the basis for calculating difficulty, for example to calculate the surface conditions of the body. For example, a thin layer of graphene or other material.

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