Effects Of Electron-Electron Interactions On The Dynamics Of Polaron In Polymers

Conjugated polymers as the new materials have a good development foreground owing to their unique properties, such as they can conduct and glow, and have advantages of simple technology, flexibility, low cost etc.. Which are different from inorganic materials, the carriers in polymers are not traditional electrons and holes, but with internal lattice structure of the nonlinear elementary excitations, such as soliton, polaron, bipolaron etc..Since 1970’s, Su, Schrieffer and Heeger have found the Su–Schrieffer–Heeger(SSH) model. The model seizes the characteristics of organic materials electron-lattice coupling and has a very good description of some physical properties in organic polymer. In the later years, Bishop, Sun and Xie et al have extended the SSH Hamiltonian to study on static properties of excitations and their dynamic processes. For example, in polymerbased light-emitting diodes, it has been generally accepted that injected charge from the metal electrodes deforms the polymer chain to form a polaron, as charge carrier; the polaron transports under the influence of an external electric field. When a positively charged polaron meets a negatively charged one, they will recombine to form a neutral polaron exciton. Then, the exciton decays radiatively to emit a photon. Obviously, the transportation of polarons plays an important role in the optoelectronic devices based on conjugated polymers. Actually, the organic materials not only have strong electron-lattice interactions, but also important electron-electron interactions. However, that in previous works, only the effect of electron-lattice interactions has been considered and of electron correlation has been ignored.Based on the SSH model and Pariser–Parr–Pople(PPP) model, by using the multiconfigurational time-dependent Hartree-Fock(MCTDHF) formalism combined with a non-adiabatic molecular dynamics method, we investigate the effect of electron-electron interactions on the properties of a charged polaron in conjugated polymers systems, especially, the long-range effect of electron-electron interactions on the dynamic properties of polaron. The localization, velocity and dissociation of the polaron will vary with the onsite electron-electron interactions U and the long-range electron-electron interactions.Using numerical simulations, we find that:(1) In a simple Hubbard model of polaron, only the on-site electron-electron interactions U is taken into consideration. As U increasing, the localized degree of polaron increases, leading to the saturated velocity of polaron decreases monotonously;(2) When the on-site electron-electron interactions U is fixed, with increasing of the long-range electron-electron interactions, the saturated velocity of polaron decreases and then with increasing of the long-range electron-electron interactions, the saturated velocity of polaron increases. It is that the above-mentioned relationship is non-monotone. The localized degree of polaron increased and the effective mass of polaron increased, leading to the saturated velocity of polaron decreases;(3) When the on-site electron-electron interactions and the long-range interactions exist at the same time, according to a fixed proportion, the saturated velocity of polaron decreases with increasing of the interactions potential strength, which reflects the competition exists between the two, with the on-site electron-electron interactions dominate.Polaron will be dissociated in the strong electric field, also there is a close relationship between dissociation properties of polaron and electron-electron interactions. We obtain some results:(1) When the on-site electron-electron interactions and the long-range interactions exist at the same time, according to a fixed proportion, the critical dissociation electric fields increase for polaron with increasing of the interactions potential strength;(2) When the on-site electron-electron interactions U is fixed, with increasing of the long-range electron-electron interactions, the critical dissociation electric fields of polaron increase and then with increasing of the long-range electron-electron interactions, the critical dissociation electric fields of polaron decrease. It is that the above-mentioned relationship is non-monotone.