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 TiObegin{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 TiObegin{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.     

导电高聚物MP-PPV的ps吸收谱研究

我们研究了在ps紫外脉冲激发下,导电高聚物MP-PPV溶液及薄膜的瞬态吸收谱。来自极化子和双极子的四个瞬态吸收带,在被稀释的MP-PPV溶液中被观察到,这些元激发的产生、迁移和衰变受不同实验条件的影响。     

Unconventional ferromagnetism and transport properties of (In,Mn)Sb dilute magnetic semiconductor

Narrow-gap higher mobility semiconducting alloys In_1-xMn_xSb were synthesized in polycrystalline form and their magnetic and transport properties have been investigated. Ferromagnetic response in In_0.98Mn_0.02Sb was detected by the observation of clear hysteresis loops up to room temperature in direct magnetization measurements. An unconventional (reentrant) magnetization versus temperature behavior has been found. We explained the observed peculiarities within the frameworks of recent models which suggest that a strong temperature dependence of the carrier density is a crucial parameter determining carrier-mediated ferromagnetism of (III,Mn)V semiconductors. The correlation between magnetic states and transport properties of the sample has been discussed. The contact spectroscopy method is used to investigate a band structure of (InMn)Sb near the Fermi level. Measurements of the degree of charge current spin polarization have been carried out using the point contact Andreev reflection (AR) spectroscopy. The AR data are analyzed by introducing a quasiparticle spectrum broadening, which is likely to be related to magnetic scattering in the contact. The AR spectroscopy data argued that at low temperature the sample is decomposed on metallic ferromagnetic clusters with relatively high spin polarization of charge carriers (up to 65% at 4.2 K) within a cluster.     

温度对于量子线强耦合极化子振动频率的影响

采用线性组合算符和幺正变换法计算了量子线中强耦合极化子的振动频率、基态能量、基态自陷能随温度、电子-声子耦合强度以及受限长度的变化。我们发现振动频率、基态能量、基态自陷能都是温度及耦合强度的函数,且随着温度的增加而增大;受限长度也随温度及耦合强度的增加而增大,但是当温度增大到一定值时,随着温度的增加耦合强度在减小。     

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.     

Rashba效应影响下量子点中弱耦合束缚极化子的性质

采用改进的线性组合算符和幺正变换的方法研究了Rashba效应影响下量子点中弱耦合束缚极化子的性质,导出了Rashba效应影响下量子点中弱耦合束缚极化子的振动频率、有效质量、基态分裂能和相互作用能。数值计算结果表明随Rashba自旋-轨道耦合常数的增加,由于声子作用产生的附加能量能对零磁场时自旋分裂能的影响占有绝对优势。库仑势对束缚极化子的基态能量的影响同时也占有绝对优势。所以,研究Rashba自旋轨道相互作时声子的影响不可忽略。