Ground state diagram of a 1D electron-phonon system

The ground states of a quasiparticle (electron, hole or exciton) are invest igated in a one-dimensional (1D) molecular chain within the variational app roach with account of quasiparticle interaction with acoustical and optical phonons. The ground state diagrams are obtained, which show the intervals of the values of dimensionless electron-phonon coupling constant, and nonad iabaticity parameter, which correspond to the regimes of an almost free ele ctron state, small polaron, and spontaneously localized (large polaron or s oliton-like) state, respectively. The creation of autolocalized states has a threshold with respect to the value of electron-phonon interaction. Such states correspond to the minimum of energy within some finite interval of t he values of electron-phonon coupling constants, the critical values of whi ch depend on the nonadiabaticity parameters of each phonon mode. It is show n that the presence of the second phonon mode enhances the stability of the autolocalized states as compared with the single mode case, and expanses t he region of soliton existence in the one-mode nonadiabatic regime. (C) 200 0 Elsevier Science S.A. All rights reserved.