Investigation of the Fröhlich model by the method of functional derivatives

The equations of motion for correlation functions of the Fröhlich model are investigated. The equations are solved with the aid of the assumption that the triple correlations in the phonon system are negligible. Two kinds of solutions, namely, the zone solution and the polaron solution, are obtained for this case. Criterions of the validity of truncations performed usually in the investigations of the Fröhlich model are established. The structure of polaron is considered and the influence of the frequency correction to the Hamiltonian on the kinetic properties of the system are investigated.