The ground state of an electron or exciton in the Holstein model

The ground state of a quasiparticle (exciton, electron or hole) interacting with dispersionless optical vibrations in a one-dimensional chain is investigated using the variational approach. The phase diagram for the quasiparticle states depending on the values of the parameters of the system, such as the nonadiabaticity parameter and the electron-phonon coupling constant, is obtained. A comparison of the results with experimental data is given