基态非简并聚合物中的极化子和双极化子的动力学(Ⅰ)--弱电场下研究

文中模拟了在基态非简并聚合物中的极化子和双极化子在弱电场中的运动,研究了在不同简并参数的系统中极化子和双极化子的动力学稳定性,发现在同一个系统中,双极化子比极化子的运动速度慢,晶格振荡小; 在简并参数大的系统中,极化子和双极化子的运动速度都变慢.极化子和双极化子在弱电场下都存在饱和速度,达到饱和速度后, 电场的能量发生了转换.     

基态非简并聚合物中的极化子和双极化子的动力学(Ⅱ)--强电场下研究

本文模拟了基态非简并聚合物中的极化子和双极化子在强电场中的运动 ,研究了在不同简并参数的系统中极化子和双极化子的动力学稳定性,发现在强场下简并参数对极化子的稳定性影响不大,极化子晶格畸变的运动滞后于电子的运动,价带上的电子在强电场的激发下参与导电.双极化子在简并参数大的系统中较为稳定.     

聚对苯撑[poly(p-phenylene)]的基态、极化子和双极化子激发态

本文在紧束缚模型基础上,对聚对苯撑类材料提出一简单的哈密顿量,并计算了系统的能带结构,给出基态、极化子、双极化子激发态,得到了双极化子比两个单极化子更容易激发这一重要结论。在能带中除发现能隙内的两个极化子定域能级外,还发现导带和价带都要发生二劈裂,带边上出现浅能级,它们对应的电子态均是定域的。 关键词：     

基态简并聚合物中极化子对的碰撞研究

基于紧束缚的Su-Schrieffer-Heeger(SSH)模型,利用非绝热的动力学方法,研究了基态简并聚合物中空穴极化子和电子极化子的碰撞过程.研究发现,弱电场下两个极化子碰撞分开再相遇形成孤子对,中等强度电场下它们碰撞分开后成为两个准粒子,强电场下空穴极化子和电子极化子碰撞后直接解离.     

极化子和双极化子在齐聚物中的稳定性

导电聚合物中的元激发稳定性问题对于认识和理解有机材料中的自旋极化输运现象是极其重要的.针对目前存在的极化子与双极化子之间的争论,本文从半经验的Austin Model 1(AM1)方法出发,对齐分子噻吩的掺杂态进行了研究.通过对极化子和双极化子体系能量的比较,发现双极化子可以转换为极化子,从而揭示出在有机半导体材料中可以实现自旋极化输运.     

固体中的极化子与双极化子

离子晶体通常具有较高的介电常数,带电粒子在晶体中会引起介电极化,其作用相当于一个可以束缚粒子的势阱.若粒子在势阱中的状态是稳定的,就有可能形成所谓的极化子与双极化子.本文采用一种简化的处理方法,将晶体材料当作各向同性的均匀介质,主要利用经典物理图像和三维量子谐振子模型,分别计算了介质中极化子与双极化子的基态能量,并进行了简要的理论分析.     

过苯胺黑聚合物的双极化子态

利用改进的Ginder-Epstein模型研究聚苯胺黑的双极化子态,给出其键序波幅、芳环扭角、电子能级、理论吸收谱和电荷分布,并与极化子进行对比.结果发现双极化子激发能为3.08 eV,晶格驰豫宽度涉及12格点与极化子相当;键交错驰豫深度大约为极化子的2倍,畸变中心芳环扭角高达68.35°大于极化子中心扭角的2倍.两个能隙态几乎简并,吸收谱低能峰为1.6 eV.     

过苯胺黑聚合物的双极化子态

利用改进的Ginder-Epstein模型研究聚苯胺黑的双极化子态, 给出其键序波幅、芳环扭角、电子能级、理论吸收谱和电荷分布,并与极化子进行对比。结果发现双极化子激发能为3.08eV, 晶格驰豫宽度涉及12格点与极化子相当;键交错驰豫深度大约为极化子的2倍,畸变中心芳环扭角高达68.35°大于极化子中心扭角的2倍。两个能隙态几乎简并,吸收谱低能峰为1.6eV。     

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     

二维极化子在磁场中的基态能量

谐振子算符的代数运算方法被用于研究磁场中同时与表面光学声子及表面声学声子相互作用的二维电子。得到二维极化子在强磁场中直至四级微扰的基态能量以及它在任意强经磁场中的二级微扰基态能量表达式。结果发现,对磁场中二维极化子基态能量的影响中,表面声学声子有着与表面光学声子同样的甚至更为突出的贡献,是不容忽视的。 关键词：     

Dynamics of interchain delocalized polarons in polymers

Polaron dynamics in a system of highly ordered conjugated polymer chains is investigated based on the tight binding model. With the interchain coupling enhancing,it takes longer time for the electron added to the system to induce a localized polaron state. Beyond a certain strength of the interchain coupling,the electron evolves into a two-dimensional delocalized polaron state. Dynamical simulations suggest that the well-ordered organic molecule systems with two-dimensional polarons exhibit higher mobilitie...     

杂质离子对有机共轭聚合物中极化子动力学性质的影响

基于一维紧束缚Su-Schrieffer-Heeger模型, 采用分子动力学方法, 讨论了杂质势的强度和杂质之间的距离对电子和空穴极化子动力学性质的影响. 研究结果表明: 1)当杂质势强度保持不变时, 两杂质离子之间的距离(d)在2-16个晶格常数变化时, 电子极化子的平均速度大于空穴极化子的平均速度, 这是由于电子、空穴极化子与杂质势的库仑作用不同而产生的差异, 同时极化子的平均速度随d的增加而增大; 若继续增加杂质离子之间的距离, 电子和空穴极化子的平均速度几乎保持不变, 仅有一些微小的振荡, 这是由于不同距离的杂质离子对电子和空穴极化子产生的势垒或势阱的叠加效果不同而引起的; 2)保持两杂质离子之间的距离不变时, 随着杂质势强度的增大, 电子和空穴极化子的平均速度均减小, 且空穴极化子的平均速度减小趋势更明显.     

有机高分子中光生极化子的物理机制

有机聚合物中光生载流子（荷电极化子）产生的物理机制是一个非常重要的物理问题，但一直存在争议，文章介绍了作者对此问题的最新研究结果：荷电极化子和中性激子一样，是由光激发直接产生的，而不是激子解体的结果，其生成时间在100fs的量级．荷电极化子的量子产率约为25％，并且与激发能量无关，与实验观测的结果一致．     

二维链间扩展的极化子动力学研究

基于扩展的SSH模型,研究了有序耦合聚合物链系统中的极化子动力学,包括极化子的形成过程及其在外场下的输运.发现,当聚合物链间的耦合较强时,注入到系统中的电子会诱发二维链间扩展的极化子态,分布在多条聚合物链上.另外,动力学模拟表明,与一维链内定域极化子相比,在相同的电场强度下二维极化子具有更大的运动速度,这与实验结果一致. 关键词： 链间扩展极化子 链间耦合     

Effects of polarons on static polarizabilities and second order hyperpolarizabilities of conjugated polymers

According to the one-dimensional tight-binding Su-Schrieffer-Heeger model,we have investigated the effects of charged polarons on the static polarizability,α xx,and the second order hyperpolarizabilities,γ xxxx,of conjugated polymers.Our results are consistent qualitatively with previous ab initio and semi-empirical calculations.The origin of the universal growth is discussed using a local-view formalism that is based on the local atomic charge derivatives.Furthermore,combining the Su-Schrieffer-Heeger model and the extended Hubbard model,we have investigated systematically the effects of electron-electron interactions on α xx and γ xxxx of charged polymer chains.For a fixed value of the nearest-neighbour interaction V,the values of α xx and γ xxxx increase as the on-site Coulomb interaction U increases for U U c and decrease with U for U U c,where U c is a critical value of U at which the static polarizability or the second order hyperpolarizability reaches a maximal value of α max or γ max.It is found that the effect of the e-e interaction on the value of α xx is dependent on the ratio between U and V for either a short or a long charged polymer.Whereas,that effect on the value of γ xxxx is sensitive both to the ratio of U to V and to the size of the molecule.     

Dynamics of photogenerated polarons in conjugated polymers

Within a tight-binding electron-phonon interacting model, we investigate the dynamics of photoexcitations to address the generation mechanism of charged polarons in conjugated polymers by using a nonadiabatic evolution method. Besides the neutral polaron exciton which is well known, we identify a novel product of lattice dynamic relaxation from the photoexcited states in a few hundreds of femtoseconds, which is a mixed state composed of both charged polarons and neutral excitons. Our results show that the charged polarons are generated directly with a yield of about 25%, which is independent of the excitation energies, in good agreement with results from experiments. Effects of the conjugation length are also discussed.     

Effects of polarons on static order hyperpolarizabilities polarizabilities and second of conjugated polymers

According to the one-dimensional tight-binding Su-Schrieffer-Heeger model, we have investigated the effects of charged polarons on the static polarizability, axx, and the second order hyperpolarizabilities, γxxxx, of conjugated polymers. Our results are consistent qualitatively with previous ab initio and semi-empirical calculations. The origin of the universal growth is discussed using a local-view formalism that is based on the local atomic charge derivatives. Furthermore, combining the Su Schrieffer-Heeger model and the extended Hubbard model, we have investigated systematically the effects of electron-electron interactions on αxx and γxxxx of charged polymer chains. For a fixed value of the nearest-neighbour interaction V, the values of αxx and γxxxx increase as the on-site Coulomb interaction U increases for U 〈 Uc and decrease with U for U 〉 Uc, where Uc is a critical value of U at which the static polarizability or the second order hypcrpolarizability reaches a maximal value of αxx or γxxxx. It is found that the effect of the e-e interaction on the value of αxx is dependent on the ratio between U and V for either a short or a long charged polymer. Whereas, that effect on the value of γxxxx is sensitive both to the ratio of U to V and to the size of the molecule.     

Instability of polarons and bipolarons in conducting polymers at various 3-d ordering types

Interchain electron hopping t_⊥ in conducting polymers with the small confinement parameter γ leads to the antiferromagnetic (AB) 3-d ordering of the dimerization pattern only at 2t²_γ >γΔ² (2Δ being the Peierls gap), otherwise the ferromagnetic (AA) one occurs. Polarons (Ps, υ = 1) and bipolarons (BPs, υ = 2) stability areas: t_⊥/Δ<t_c (υ,γ) are found in the phase plane “t_⊥ vs γ” with critical t_c being larger in the AB phase and for BPs. At the AA-AB transition interface, “deconfinement” of kink-solitons is possible. Photogeneration of Ps and BPs may proceed via metastable free states separated by the self-trapping barriers (STBs) which are also different in AA and AB (in the latter STBs exist even in 2-d systems) and are lower for BPs.     

钙钛矿锰氧化物中的极化子研究

钙钛矿锰氧化物(以下简称锰氧化物,如La_1-xSr_xMnO₃等,x为掺杂浓度)因其优异的电、磁性质受到人们广泛的关注,但是对于其材料内部载流子性质的认识至今仍没有统一定论.本文基于锰氧化物内Mn—O链的特点,建立一维紧束缚模型,对锰氧化物载流子的性质展开研究.发现在掺杂浓度x=0.5时,系统处于铁磁态,自旋能级完全劈裂,价带和导带之间存在带隙,所有电子态呈现扩展行为.进一步掺杂,将出现局域电子态,同时伴随着晶格的局域畸变,形成所谓的极化子.伴随着极化子的出现,带隙中出现极化子深能级.极化子携带的电荷量越多,形成的晶格缺陷越深,局域能级也越深.当极化子的电荷量继续增加时,极化子解离,载流子倾向于形成能量更低的正反"孤子"对.