ONE-DIMENSIONAL ELECTRON-PHONON SYSTEM AT ARBITRARY COUPLING-CONSTANT

The ground state of a quasi-particle (exciton, electron or hole) inter acting with optical and acoustic phonons in a one-dimensional chain, i s investigated using a variational method. The phase diagrams are obta ined which show the regions of the electron-phonon coupling constant a nd nonadiabaticity parameter where the ground state of a quasiparticle is described as almost free electron state, small polaron, or spontan eously localized state. It is shown that the formation of a soliton-li ke state has a threshold with respect to the value of electron-phonon interaction. The corresponding critical value of the coupling constant increases with the nonadiabaticity parameter increasing.