Spectrum and eigenfunctions of Schroedinger operator with point-like potential of the homogeneous lattice type in three-dimensional space

Spectrum and all the eigenfunctions of the Schroedinger operator with point-like potential of the homogeneous endless square lattice in three-dimensional space were studied. The completeness property of the system of eigenfUnctions in three-dimensional α2(R3) space was formulated. It is shown that the energy operator has noo discrete spectrum. Formulae for effective masses of the operator and Fermi surface are given