The statement of the problem of scattering of band electrons in an atomic chain by impurities in the approximation of potentials of zero radius
... In order to describe zone electrons the Bloch functions are constructed with respect to symmetry consideration. In addition, zero range potential approximation is used to model both atoms in chain and impurity atoms.
Botman S. A., Leble S. B.
Bloch wavefunction, scattering, impurity, zero range potential
29-34