长程电子关联对聚噻吩中极化子的影响

采用扩展的SSH模型,加上电子相互作用和长程电子关联,用自洽迭代的方法研究了聚噻吩链中的极化子问题,计算了电子相互作用和长程电子关联对极化子位形和电荷密度的影响,获得了长程电子关联使极化子位形变小,极化子区域变窄,电荷密度震荡减弱,对聚合物中电子的输运的影响不能忽略的有益结果.     

Hole polarons in poly(G)-poly(C) and poly(A)-poly(T) DNA molecules

The polaron might play an important role in the process of charge migration through duplex DNA stack. In the present work, we investigate properties of hole polarons in DNA molecules containing identical base pairs, such as poly(G)-poly(C) and poly(A)-poly(T), An extended tight-binding model (extended Su-Schrieffer-Heeger model), which involves the effect of an electric field in the direction of DNA stack, will be introduced. The transfer integral and electron-phonon coupling parameters in this model are obtained according to ab initio calculation for different base pair dimers. Calculations reveal that the polaron in poly(A)-poly(T) has a wider shape and a higher mobility under a specific electric field than that in poly(G)-poly(C) DNA stack.     

Optically detected magnetic resonance studies of luminescence‐quenching processes in π‐conjugated materials and organic light‐emitting devices

It is widely recognized that nonradiative quenching of excitons by other excitons and polarons become the dominant decay mechanism of these excitons at high excitation densities. These quenching processes cause the roll‐off in the efficiency of organic light‐emitting devices (OLEDs) and prevent lasing at high injection current densities. This review presents the optically‐detected magnetic resonance (ODMR) evidence for these photoluminescence‐ and electroluminescence‐quenching processes. And while it provides such evidence for quenching of singlet excitons by polarons and triplet excitons, it reveals the central role of the strongly spin‐dependent annihilation of triplet excitons by polarons, since under normal excitation conditions the steady‐state polaron and triplet exciton populations are 100–10⁴ times the singlet exciton population. In addition, it also suggests that quenching of singlet excitons by bipolarons, likely stabilized by a counterpolaron or countercharge at specific sites, may also be a significant quenching mechanism that also affects the charge transport properties.     

盘型量子点中极化子的温度效应

在考虑电子与体纵光学声子强耦合的条件下,通过求解能量本征方程,得出了盘型量子点中电子的基态能量、第一激发态能量及其相应的本征波函数;采用幺正变换和元激发理论方法研究了圆盘型量子点的声子效应,并讨论了温度对量子盘中极化子性质的影响。数值计算表明：在温度较低时,声子不能被激发,温度对能量无影响,当温度较高时,声子能够被激发,且温度愈高,被激发的声子数愈多,极化子能量愈大;结果还表明基态能量随着电子-声子耦合强度的增大而减小,随量子盘半径的增大而减小. 说明量子盘具有明显的量子尺寸效应。     

共轭高聚物中极化子形成的自洽迭代收敛性

用自洽迭代的方法模拟了一维共轭高聚物链中极化子的形成,得出有机物链的初始晶格位形与自洽迭代收敛性的关系。对于初始晶格位形为键长有规律交错变化的一维晶格,闭链的收敛精度远高于开链的收敛精度,表明有机物链越长收敛越慢。对于闭链,降低晶格的对称性,有利于自洽迭代收敛于极化子。在有机物链中出现杂质的情况下,我们发现杂质所处的位置同收敛性密切相关,当掺杂发生在有机物链的中心附近区域时,自洽迭代单调收敛;而当掺杂发生在其它区域时,收敛过程出现波动性,导致收敛过程变慢。我们的研究表明,一维有机分子链中载流子的生成同初始晶格的位形与分子链所处的环境密切相关,这预示着在更复杂的有机物结构中,可能存在新型的复合载流子。     

Constrained Density Functional Theory Plus the Hubbard U Correction Approach for the Electronic Polaron Mobility: A Case Study of TiO2?

The formation and migration of polarons have important influences on physical and chemical properties of transition metal oxides. Density functional theory plus the Hubbard \begin{document}$U$\end{document} correction (DFT+\begin{document}$U$\end{document}) and constrained density functional theory (cDFT) are often used to obtain the transfer properties for small polarons. In this work we have implemented the cDFT plus the Hubbard \begin{document}$U$\end{document} correction method in the projector augmented wave (PAW) framework, and applied it to study polaron transfer in the bulk phases of TiO\begin{document}$_2$\end{document}. We have confirmed that the parameter \begin{document}$U$\end{document} can have significant impact on theoretical prediction of polaronic properties. It was found that using the Hubbard \begin{document}$U$\end{document} calculated by the cDFT method with the same orbital projection as used in DFT+\begin{document}$U$\end{document}, one can obtain theoretical prediction of polaronic properties of rutile and anatase phases of TiO\begin{document}$_2$\end{document} in good agreement with experiment. This work indicates that the cDFT+\begin{document}$U$\end{document} method with consistently evaluated \begin{document}$U$\end{document} is a promising first-principles approach to polaronic properties of transition metal oxides without empirical input.     

准二维强耦合激子能量的温度依赖性

采用线性组合算符法和LLP变分法研究了晶格热振动和极化子效应对量子阱中激子与界面光学(IO)声子强耦合又与体纵光学(LO)声子弱、中耦合体系的基态和激发态的影响,推导出作为量子阱宽和温度函数的激子基态能量的移动和第一内部激发态能量的移动的表达式,以AgCl/AgBr/AgCl量子阱为例进行了数值计算.结果表明,由激子IO声子强耦合所产生的激子基态能量移动和第一内部激发态能量移动随温度的升高而增大,而由激子-LO声子弱、中耦合所产生的激子基态能量移动和第一内部激发态能量移动随温度的升高而减小.     

抛物量子阱中的束缚极化子:分维变分方法

采用分维变分方法讨论了有限深抛物量子阱中束缚极化子的束缚能,得到了束缚能随阱宽的变化关系,并给出了声子对束缚能的贡献随阱宽的变化曲线.数值计算的结果表明,束缚极化子的束缚能随阱宽的增大存在一极大值,电子一声子的相互作用使束缚极化子的束缚能显著降低,声子的贡献不可忽略.     

库仑场对量子点中极化子性质的影响

采用基于逐次正则变换的变分方法,利用单模压缩态变换处理包含声子产生湮灭算符的双线性项,研究了抛物量子点中束缚极化子的性质. 得到了在电子-体纵光学声子强﹑弱耦合极限下抛物量子点束缚极化子的基态能量及电子周围平均声子数. 讨论了受限长度,电子-体纵光学声子耦合常数,库仑结合参数与基态能量和平均声子数之间的依赖关系.     

层状钙钛矿铁电薄膜中铁电极化子研究

用PLD方法在铂金硅衬底制作了高质量的SrBi2Ta2O9(SBT)铁电薄膜样品．在10到300K的低温范围，研究了SBT薄膜的电子输运特性，分析了其传导机制．结果显示在SBT铁电薄膜中存在两种导电机制．根据SBT层状结构，两种导电机制分为：被限制在Bi—O层内的内输运，和能够穿过Bi—O层的外输运．首次观察到作为内传导载流子的铁电极化子的电输运行为．在SBT薄膜中铁电极化子的热激活能Eα～0．0556eV．研究结果为SBT薄膜具有极低漏电流提供了一种解释．