扩展苯基衍生物分子器件的电子输运的理论研究

通过结合杂化密度泛函和前线轨道理论与弹性散射格林函数方法研究了三种苯基衍生物分子器件的电子输运性质. 基于杂化密度泛函方法计算扩展分子电子结构的基础上, 计算了苯基衍生物三分子结的输运性质. 计算结果表明, 在低偏压下, 电流与电压呈线性变化; 分子结的电阻的对数与苯环的数目呈线性增加关系.     

CO分子结点电子结构和输运性质的第一原理研究

采用基于密度泛函理论(DFT)的非平衡态格林函数方法(NEGF), 计算了CO分子结点低偏压下的电流和电导. 通过系统透射谱、投影态密度(PDOS)以及分子自洽投影哈密顿量(MPSH)本征态的分析将透射通道与局域分子轨道联系起来, 从系统电子结构解释了其传输性质. 讨论了电荷转移对系统电导的影响.     

Al-C60-Al分子结电子输运特性的第一性原理计算

利用基于密度泛函理论的格林函数方法, 计算了Al-C60-Al分子结的电子输运特性. 考虑了C60分子在铝电极表面的原子结构弛豫, 计算结果表明共振传导是Al-C60-Al分子结电子输运的主要特征, 在费米能级附近的电导约为1.14G0 (G0=2e2/h). 投影态密度(PDOS)分析表明, Al-C60-Al分子结的电子输运主要通过C60分子的最低空分子轨道(LUMO)和次低空分子轨道(LUMO+1)进行. 讨论了C60分子和铝电极之间距离的变化对其电子输运特性的影响.     

单分子器件电子输运性质的理论研究

对当前单分子器件的理论和实验的研究进展作了简短评述,并简要介绍电子输运理论,最后给出一个基于非平衡态格林函数电子输运理论的全自洽方法,研究单个水分子在Au(111)电极之间的输运性质的计算实例.研究结果表明由于水分子与电极之间存在较强的杂化作用,水分子的分立能级间距大,在小偏压范围内,水分子的特征已经被淹没在杂化能级之中.体系的电势变化主要发生在水分子局域区间,其电子输运行为主要是一个单通道过程.     

正三角锯齿型石墨烯的电子输运特性

利用密度泛函理论和非平衡格林函数方法, 系统研究了正三角锯齿型石墨烯的电子输运特性. 研究表明: 正三角石墨烯的电流-电压(I-V)特性及整流效应与几何尺寸、边缘吸附原子的类型密切相关, 在其边缘吸附H原子和S原子的情况下, 小的正三角石墨烯有大的电流, 但有小的整流比; 改变边缘吸附原子的类型(用O原子替换H原子), 电流增大, 但其整流效应明显变低. 分析表明, 这种整流是由于正三角石墨烯前线轨道的空间分布不对称以及在正、负偏压下分子能级的非对称移动所致. 我们的研究对于认识正三角石墨烯的基本物性(电子结构及器件应用)有重要意义.     

分子旋转对分子器件电子输运性质的影响

利用基于非平衡格林函数和密度泛函理论相结合的第一性原理计算方法,研究了一种可旋转分子跨接在金电极上的电子输运性质。计算结果表明:分子中的转子与定子间的旋转角度可以有效调控分子器件的电子输运性质。当夹角从30°变化到150°,分子器件的导电性呈现出增强、减弱的震荡变化。此外,当夹角变化到90°,分子器件的电流电压曲线打破其他角度呈现的线性变化特性,其电流值在2.4 V以后随着电压的增大而减小,表现出强烈的负微分电阻效应。     

二苯乙炔分子导线的电子输运性质

利用第一性原理非平衡态格林函数方法研究了不同构象下二苯乙炔分子导线的电子输运性质. 从分子轨道空间分布和透射谱等方面讨论了外加偏压下分子构象对电子传递特性的影响及内在机理. 结果表明, 随着分子扭转角的增加, 分子的LUMO-HOMO能隙增加, 透射峰显著降低; 外加偏压下, 分子的HOMO分布向低电势端移动, LUMO向高电势端移动. 电流-电压计算表明, 平面构象分子的导电性最好; 随着扭转角的增加, 分子的导电性变差; 垂直构象分子的导电性最差. 最后给出了分子导线电子传递性质与分子构象的定量关系.     

Armchair型石墨纳米带的电子结构和输运性质

利用第一性原理的电子结构和输运性质计算方法, 研究了扶手椅(armchair)型单层石墨纳米带(具有锯齿边缘)的电子结构和输运性质及其边缘空位缺陷效应. 研究发现, 完整边缘的扶手椅型石墨纳米带是典型的金属性纳米带, 边缘空位缺陷的存在对扶手椅型纳米带能带结构有一定的影响,但并不彻底改变其金属性特征.     

硅桥调控的聚茂钒体系电子结构和输运性质

利用密度泛函理论和非平衡格林函数的方法对硅桥调控后的聚茂钒体系（[V（Cp）₂（SiH₂）_n]_m（n=1（a）,n=2（b）,n=3（c）;m=∞;Cp=环戊二烯基））的电子结构和输运性质进行了研究。研究结果表明：随着硅桥的增长,V-V的铁磁性耦合变弱而反铁磁性耦合增强。a和b证实为铁磁性基态,而c更倾向为反铁磁性基态。a和b的铁磁性基态中的每个钒原子的磁距为3.0μ_B,超过钒-苯络合物或者纯聚茂钒体系的3倍。a-c的输运性质同它们的电子结构相一致,导电性变化规律为c > b > a。对于a和b,自旋向下状态的导电性略强于自旋向上状态。a和c都发生了明显的负微分电阻效应而b却没有,这主要是由于两个二茂钒的排列取向不同：a和c（SiH₂为奇数）中二茂钒呈V-型取向排列,进而导致了类似于离子键的量子点耦合,而b（SiH₂是偶数）中二茂钒是平行-型取向排列,从而导致了类似于共价键的量子点耦合。此外,由于散射区和两个电极之间的不对称耦合,a-c的导电性对电压施加方向较敏感。     

金属/分子/金属结的电子输运机理与表征

金属/分子/金属结是分子电子学中的基本单元.根据电子的相位是否发生改变,分子结中的电子输运可以分为相干输运和非相干输运两类.在实验上,分子结的表征方法可以分为电学性质表征和非电学性质表征两类.本文借助能级图,首先对分子结的电子输运机理作了简明解释.在此基础上,结合文献报道和本课题组此前的工作,对分子结的一些常用电学表征方法,包括电流-电压特性曲线、电流-时间曲线、电导统计柱状图、转变电压谱、散粒噪声测试、非弹性电子隧道谱和热电效应法进行了介绍.     

Quantum chemical investigations of the latent image formation

Having studied free silver clusters by quantum chemical calculations we now present a method to take into account the influence of a silver halide surface on adsorbed silver clusters. The model for the surface will be a silver halide cluster as frozen crystal section. The interactions are discussed in detail; a new bromide pseudopotential may be of special interest. Results with this method will be given in subsequent papers.     

Quantum chemical investigations of the latent image formation

The adsorption of Ag⁺ and Ag on a (100) AgBr surface is investigated. Interstitial subsurface sites and incomplete surfaces (with ledges and kinks) are also considered. Equilibrium geometries, adsorption energies and ionization potentials have been calculated. Migration of neutral Ag on the surface and crystal growth of AgBr are discussed, and a comparison with other theoretical results is given.     

Quantum chemical investigations of the latent image formation

The alternating process of adsorption of Ag⁺ and trapping of a photoelectron on a (100) AgBr surface is investigated by quantum chemical calculations. The results give some insight into the initial steps of the photographic process (absorption of two photons which lead to the formation of a sublatent image).     

Quantification of electron correlation effects: Quantum Information Theory vs Method of Increments

Understanding electron correlation is crucial for developing new concepts in electronic structure theory, especially for strongly correlated electrons. We compare and apply two different approaches to quantify correlation contributions of orbitals: Quantum Information Theory (QIT) based on a Density Matrix Renormalization Group (DMRG) calculation and the Method of Increments (MoI). Although both approaches define very different correlation measures, we show that they exhibit very similar patterns when being applied to a polyacetelene model system. These results suggest one may deduce from one to the other, allowing the MoI to leverage from QIT results by screening correlation contributions with a cheap (“sloppy”) DMRG with a reduced number of block states. Or the other way around, one may select the active space in DMRG from cheap one-body MoI calculations.     

Density functional theory study on electron and hole transport properties of organic pentacene derivatives with electron-withdrawing substituent

Attaching electron-withdrawing substituent to organic conjugated molecules is considered as an effective method to produce n-type and ambipolar transport materials. In this work, we use density functional theory calculations to investigate the electron and hole transport properties of pentacene (PENT) derivatives after substituent and simulate the angular resolution anisotropic mobility for both electron and hole transport. Our results show that adding electron-withdrawing substituents can lower the energy level of lowest unoccupied molecular orbital (LUMO) and increase electron affinity, which are beneficial to the electron injection and ambient stability of the material. Also the LUMO electronic couplings for electron transport in these pentacene derivatives can achieve up to a hundred meV which promises good electron transport mobility, although adding electron-withdrawing groups will introduce the increase of electron transfer reorganization energy. The final results of our angular resolution anisotropic mobility simulations show that the electron mobility of these pentacene derivatives can get to several cm(2) V(-1) s(-1), but it is important to control the orientation of the organic material relative to the device channel to obtain the highest electron mobility. Our investigation provide detailed information to assist in the design of n-type and ambipolar organic electronic materials with high mobility performance.     

Stacking effect of polyfluorene on the chemical shift and electron transport

We investigate the structures, NMR chemical shifts, absorption spectra, frontier molecular orbitals, and transition density matrices of pi-stacked polyfluorenes by ab initio calculations. For F1-F4, we consider two different conformations, syn and anti. The simulated 1H NMR chemical shifts are in good agreement with the previous experiment, and the significantly upfielded chemical shifts explain that the fluorene moieties are stacked on each other. It is found that the relative stability for syn and anti conformers is almost equivalent in B3LYP calculations; however, the syn conformer becomes much more stable than the anti conformer in MP2 calculations, which is consistent with the experimental finding that only the syn conformers are relevant. The vertical detachment energy, which is linearly proportional to the ionization potential, shows the same size dependence as the previous experiment. The electron attachment energy decreases exponentially as the size increases, which implies that the electron transport would be possible even for long chains such as F3 and F4. This was evident from the frontier molecular orbitals (HOMO and LUMO). Also, it is found that the syn conformers are very favorable for electron transport through the pi-stacked fluorene moieties.     

Distributions of electron density in the methyltrioxorhenium molecule

Absctract The effective charges on atoms in the methyltrioxorhenium molecule were determined on the basis of the correlation between the chemical shift of¹⁷O and the energy of electron transition in absorption spectra.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp 1859–1861, July, 1996.     

硅-硫团(SiS_2)_n~+(n=4,5)的结构和振动光谱的量子化学研究

用密度泛函（ＤＦＴ） 方法研究了硅硫团簇（ＳｉＳ２） ｎ＋（ ｎ ＝ ４ ,５） 的各种可能几何构型和电子结构,并计算了相应的振动光谱,得到了（ＳｉＳ２）ｎ＋ 的形成规律,即（ＳｉＳ２）ｎ ＋ 以硅、硫交错形成四元环链的形式增长．     

Quantum chemical investigation of lanthanum doping effects in tetragonal and rhombohedral PZT materials

Structural and electronic properties of lead–zirconate–titanate (PZT) materials doped with a lanthanum (La) impurity are studied using a quantum‐chemical approach based on the Hartree–Fock theory. Performed geometry optimization in the defective crystals shows that the atomic movements are predominantly outward with respect to the impurity position. It is found that the La impurity enhances a covalent character in the chemical bonding between the Ti and O atoms, as well as the Zr and O atoms situated in the neighborhood of the defect despite the fact that the La‐O interaction remains purely ionic. The occurrence of local energy levels within the band gap of the material is analyzed in light of the available experimental data on La concentration influence upon dielectric and piezoelectric properties in these crystals. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009