Long-range Coulomb interaction effects on polarons in conjugated polymers

Combining the Su–Schrieffer–Heeger and Pariser–Parr–Pople model (SSH+PPP), we have studied the influence of electron–electron interactions on the motion and dissociation of a polaron in the presence of an electric field, with emphasis on the long-range Coulomb interactions. The multiconfigurational time-dependent Hartree–Fock (MCTDHF) formalism was used to compute the electron–electron interactions. How the saturated velocity and the critical dissociation electric field of the polaron are related to the on-site Coulomb repulsion and long-range Coulomb interactions has been investigated. It was found that the on-site Coulomb interaction does not favor the motion of a polaron. There is a critical strength of the long-range Coulomb interaction for which the polaron takes on the most localized configuration. Comparing with the results obtained using the extended Hubbard model, we found that competition between the long-range Coulomb interactions and the on-site Coulomb interaction leads to a non-monotonic dependence of both the saturated velocity and the critical dissociation electric field on the long-range Coulomb interactions.     

Efficiency Roll‐Off in Blue Emitting Phosphorescent Organic Light Emitting Diodes with Carbazole Host Materials

The efficiency roll‐off in blue phosphorescent organic light emitting diodes (OLEDs) using different carbazole compounds as the host is systematically studied. While there is no significant difference in device efficiency, OLEDs using ter‐carbazole as the host show a reduction in efficiency roll‐off at high luminance. Data from transient photoluminescence and electroluminescence measurements show that the lower triplet–triplet annihilation (TTA) and triplet–polaron quenching (TPQ) rates in devices with the ter‐carbazole host compared with other carbazole hosts are the reasons for this reduced efficiency roll‐off. It is also found that the host materials with low glass transition temperatures are more susceptible to the efficiency roll‐off problem.     

The Properties of Surface Polaron in the Semi-Infinite Polar Crystal

The effective Hamiltonian and the renormalized mass of surface polaron, where the electron is strongly coupled with the surface optical (SO) phonons but weakly or intermediately coupled with the bulk longit udinal-optical (LO) phonons, were first reviewed. The self-energy and the renormalized mass of the polaron for the polar crystals of potassium iodide, silver chloride and silver bromide are evaluated as a function of the depth Gom the crystal surface. Results of our calculation indicate that the effect of the electron-SO phonon interaction is dominant only within a very small layer from the crystal surface. Its justification awaits further experimental results.     

极性晶体膜中电子—表面声子强耦合极化子的自陷能

采用Ｈｕｙｂｒｅｃｈｔｓ线性组合算符和变分法相结合的方法,研究了极性晶体膜内电子与体纵光学声子弱耦合、与表面光学声子强耦合系统的基态能量,得到了作为膜厚和耦合常数函数的极化子的自陷能,对ＫＣｌ晶体进行了数值计算,结果表明,不同支声子与电子相互作用对极化子自陷能的贡献大不相同     

Energy Gap and Charge Transfer in Doped Quasi-One-Dimensional π-Conjugated Organic Ferromagnetic

The effects of polarons along main chain and spin-soliton-like along side-radical lattice in doped quasi-one-dimensional π-conjugated organic ferromagnets are studied by selfconsistent method. It is shown that the gap of spin-down and spin-up mid energy bands of the system decreases because new energy levels of localization states appear. The stability of organic ferromagnetic system is weakened with decreasing of the gap. In addition, it is also shown that there is charge transfer between main chain and side-radical lattice of the doped system.     

A New Variational Study for Two-Site Holstein Model

A variational approach is developed to study the groundstate (GS) of the two-site Holstein model. By the extended coherent state, where the more phonon correlations are easily incorporated, we can get the very accurate ground state energy for all electron-phonon coupling range in typical values of hopping integral t=0.5,1.1, and 2.1 (in units of phonon frequency ω₀), which covers the crossover region from antiadiabatic limit to the adiabatic limit. Within a very wide t range [0,2.7], the exact results for the GS energy are obtained with the twelfth (fourteenth) order corrections to the zeroth order wave function. Moreover, the present approach is more concise than any other analytical ones in this field, and hopefully can be easily generalized to many other Holstein models.     

Mean-field properties of impurity in Bose gas with three-body forces

We exactly analyze, on the mean-field level, the low-momentum properties of a single impurity atom loaded in the dilute one-dimensional Bose gas with two- and three-body short-range interactions. Particularly the Bose polaron binding energy and the quasiparticle residue are calculated for the considered system in the broad region of parameters change. We also explore the generic mean-field formula for the polaron effective mass which was shown to depend on the density profile of bath particles with a motionless impurity immersed.     

基态非简并导电聚合物——坐标空间研究

通过引入简并破缺项,建立了非等势垒Kronig-Penney方势阱模型,在实坐标空间中研究了基态非简并聚合物——顺式聚乙炔的基态及其激发态,并与紧束缚模型所得到的结果进行了比较.给出了体系的电子态、电荷密度等在实坐标空间的分布特征.发现在坐标空间研究可以更加准确地反映体系的电子态密度、电子空间密度分布等特征. 关键词： 聚合物 方势阱 基态 极化子     

Bound polaron in a two- and three-dimensional quantum dot for arbitrary electron–phonon coupling strength

A variational approach is presented for calculating the ground-state (GS) binding energies of an electron bound to a Coulomb impurity in a polar semiconductor quantum dot (QD) with parabolic confinement in both two and three dimensions. We perform calculations for the entire range of the electron-phonon coupling constant and the Coulomb binding parameter and for arbitrary confinement length. It is found that the polaronic effect is stronger in a two dimensions (2D) dot than in a three dimensions (3D) dot and this trend is more pronounced with the increase of the coupling constant. Furthermore, the GS binding energy increases with increasing the Coulomb binding parameter in both 2D and 3D QDs for the same electron–phonon coupling constant. The results also indicate that this effect becomes much more pronounced with decreasing dimensionality.     

Small polaron mass with a long range density-displacement type interaction

In this work renormalization of the effective mass of an electron due to a small polaron formation is studied within the framework of the extended Holstein model. It is assumed that an electron moves along the one-dimensional chain of ions and interacts with ions vibrations of a neighboring chain via a long-range density-displacement type force. By means of the exact calculations a renormalized mass of a nonadiabatic small polaron is obtained at strong coupling limit. The obtained results compared with the mass of small polaron of ordinary Holstein model. The effect of ions vibrations polarization on the small polaron mass is addressed.