Structure of a strongly coupled large polaron

We use the translationally invariant Bogolyubov—Tyablikov method to propose a polaron theory. We present calculations of autolocalised electron states for different types of interaction. The structure of these states is shown to be strongly related to the structure and details of the local phonon spectrum. We calculate this spectrum in the strong-coupling limit. Applications of the large polaron model and possibilities of experimental tests are considered for the strong coupling. We generalise the Bogolyubov—Tyablikov treatment to the strongly coupled bipolaron and give criteria of the stability and formation of the bipolaron states.