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.     

结构转变方式对光致变色分子开关输运性能影响的从头计算研究(英文)

采用密度泛函理论方法系统地研究了由不同结构转变方式引发的一系列光致变色分子在用于分子开关时的电子输运性质.对各种分子结构转变前后的最高占据轨道(HOMO)与最低空轨道(LUMO)的能级间隙(HLG)、前线轨道的空间分布、电子透射谱和投影电子态密度(PDOS)谱进行了计算和讨论.结果表明,相似的结构转变方式通常造成分子具有相似的电流开关性质,这与分子的共轭程度又有一定的关系.比较各种分子的电流开关比后发现偶氮苯结构单元具有最大的电流开关比.     

密度泛函理论研究镥二聚体低电子能态的相对稳定性、结构以及成键性质

用密度泛函理论方法研究了镥二聚体（Lu2）低能量电子态的性质,计算了电子态相对能量、平衡键长、振动频率以及基态解离能,考察了密度泛函性质、相对论有效势种类以及Hartree—Fock交换作用大小对计算结果的影响．结果表明,无论采用何种密度泛函和相对论有效势,体系的基态都为三重态,与其他一些基于分子轨道理论的从头计算方法得到的结论是一致的．另外,与分子轨道从头计算结果以及实验结果比较发现,采用杂化密度泛函理论和Stuttgart小核有效势计算得到的结果总体吻合最好．最后,特别分析研究了B3LYP计算中Hartree—Fock交换作用大小对基态键长和基态解离能的影响,发现随着交换作用的增大,键长增长,解离能减小,这是由于5d轨道杂化导致的共价成键作用减弱造成的．     

1,3-二氮杂薁类衍生物电子结构和光谱性质的理论研究

对1,3-二氮杂薁类衍生物采用密度泛函理论(DFT)在B3LYP/6-31G(d)的水平上进行了几何构型的全优化, 在此基础上探讨了分子结构和前线分子轨道能量等性质的变化规律, 采用含时密度泛函理论(TD-DFT)计算了分子的电子跃迁性质, 采用二维平面图和三维立体图来直观表示激发态的性质, 研究分子内电子转移特性. 跃迁密度矩阵的二维等高线图反映了电子-空穴相干性, 三维跃迁密度图反映了跃迁偶极矩的方向和强度, 三维电荷差异密度图说明了激发过程中分子内电子转移性质.     

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.     

烷基取代对罗丹明的电子结构与光谱的影响

在密度泛函理论(DFT)的B3LYP水平对不同烷基在不同位置取代形成的8种罗丹明化合物进行结构优化,并在此基础上应用含时密度泛函理论(TD-DFT)和单激发组态相互作用(CIS)方法分析了取代基对罗丹明的电子结构、前线分子轨道及电子光谱的影响.计算结果表明,前线分子轨道主要分布在罗丹明分子的氧杂蒽环上,罗丹明分子中两个N端的H各只有1个H被烷基取代时,最高占据轨道(HOMO)在主要共轭环分布最多,且HOMO和最低未占据轨道(LUMO)分布比例相差最小,两个N端4个H同时被甲基取代时,能隙最窄,对气相最大吸收波长红移程度最大,两个N端4个H同时被乙基取代时,气相荧光最大,发射波长最长.     

XYG3型双杂化密度泛函方法新进展：从能量到能量的解析梯度

本文回顾了现代密度泛函理论的基础,着重评述了XYG3型双杂化（XYG3typeofdoublyhybrid,xDH）泛函的最新进展,解析能量梯度的实现．XYG3是首个依照绝热途径理论建立的双杂化泛函,在具体实现上具有独特的构架．该类型泛函利用常用泛函（如B3LYP或PBE0等）作母泛函来进行自洽计算,以期获得更好的密度和轨道,然后将所得到的轨道和密度信息带入到xDH泛函中以得到最终能量．由于自洽泛函和最终能量泛函不同,因而在计算解析能量梯度时需要求解耦合微扰Kohn—Sham方程．在此基础上,还评述了xDH泛函在能量,尤其是构型优化方面的具体表现．测试的构型集包括以共价键键合的分子和非键相互作用体系的平衡结构,以及反应过渡态结构．结果表明,xDH双杂化泛函总体上给出了比母泛函更好的能量和几何构型．     

等性扩展基杂化轨道的构造

杂化轨道理论近来有了长足的发展,杂化轨道的构造方法主要有群论方法最大重叠方法,自然杂化轨道法和其它以分子轨道为基础构造杂化轨道的方法等。其中最大重叠杂化轨道不仅满足正交化条件而且能较定量地考虑到配体轨道的作用,因而已经得到广泛应用。本文在最大重叠原理的基础上得到了扩展基杂化轨道的解析形式。扩展基杂化轨道对一给定几何构型的分子M(X_1X_2…X_n),其中心原子M的n个杂化轨道与诸配体{X_i}形成一组方向键。M的杂化轨道(HO)和原子轨道(AO)可分别作为该分子对称操作群的表示之基。这两种不同基的表示进行约化之后,属于同一不可约表示的HO和AO是线性相     

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.     

Al8P8团簇环状结构与性质的密度泛函理论研究

用密度泛函理论(DFT)中的杂化密度泛函B3LYP方法, 在6-31G*水平上对Al8P8团簇的环状结构进行了几何结构优化, 并在同一水平上计算了Al8P8团簇的电子结构、振动特性及极化率和超极化率. 用自然键轨道(NBO)方法分析了成键性质, Al8P8团簇中离子键和共价键共存, 而且在不同轨道中原子间成键有不同的杂化方式. 计算结果表明: 优化后的Al8P8团簇为双层环状结构; 价电子态密度显示其电子结构具有半导体的性质; 最强的IR和Raman谱峰分别位于530.65 cm-1和366. 54 cm-1处.     

氢键对分子器件电学特性的影响

利用密度泛函理论和弹性散射格林函数方法,研究了被不同官能团取代后的联苯分子的电输运特性.计算结果表明,由于氢键的影响,使得分子的电子结构发生了变化,特别是对电子在分子结内的跃迁几率影响较大,从而直接影响了分子器件的伏安特性.     

Charging energy and barrier height of pentacene on Au(111): a local-orbital hybrid-functional density functional theory approach

We analyze the pentacene/Au(111) interface by means of density functional theory (DFT) calculations using a new hybrid functional; in our approach we introduce, in a local-orbital formulation of DFT, a hybrid exchange potential, and combine it with a calculation of the molecule charging energy to properly describe the transport energy gap of pentacene on Au(111). Van der Waals forces are taken into account to obtain the adsorption geometry. Interface dipole potentials are also calculated; it is shown that the metal/pentacene energy level alignment is determined by the potential induced by the charge transfer between the metal surface and the organic material, as described by the induced density of interface states model. Our results compare well with the experimental data.     

Encapsulation effect of π-conjugated quaterthiophene on the radial breathing and tangential modes of semiconducting and metallic single-walled carbon nanotubes

We developed a hybrid approach, combining the density functional theory, molecular mechanics, bond polarizability model and the spectral moment's method to compute the nonresonant Raman spectra of a single quaterthiophene (4T) molecule encapsulated into a single-walled carbon nanotube (metallic or semiconducting). We reported the optimal tube diameter allowing the 4T encapsulation. The influence of the encapsulation on the Raman modes of the 4T molecule and those of the nanotube (radial breathing modes and tangential modes) are analyzed. An eventual charge transfer between the 4T oligomer and the nanotube is discussed.     

Nonequilibrium GW approach to quantum transport in nano-scale contacts

Correlation effects within the GW approximation have been incorporated into the Keldysh nonequilibrium transport formalism. We show that GW describes the Kondo effect and the zero-temperature transport properties of the Anderson model fairly well. Combining the GW scheme with density functional theory and a Wannier function basis set, we illustrate the impact of correlations by computing the I-V characteristics of a hydrogen molecule between two Pt chains. Our results indicate that self-consistency is fundamental for the calculated currents, but that it tends to wash out satellite structures in the spectral function.     

Vibrational spectroscopic and conformational studies of 1-(4-pyridyl)piperazine

Possible stable conformers of the 1-(4-pyridyl)piperazine (1-4pypp) molecule were experimentally and theoretically studied by FT-IR and Raman spectroscopy. FT-IR and Raman spectra were recorded in the region of 4000–200 cm⁻¹. Optimized geometric structures related to the minimum on the potential energy surface were investigated by the B3LYP hybrid density functional theory method using the 6-31G(d) basis set. Comparison of the experimental and theoretical results indicates that the density functional B3LYP method provides satisfactory results for the prediction of vibrational wavenumbers and structural parameters and equatorial-equatorial (e-e) isomer is supposed to be the most stable form of the 1–4pypp molecule.     

A Density Functional Theory Study on Electronic Structure and Second—order Nonlinear Optical Properties of Some Push—Pull Molecules

Time-dependent density-functional theory(TDDFT)has been applied to calculate the electronic structure and second-order nonlinear optical(NLO) properties of some organic molecules.The two-dimensional(2-D)charge transfer charateristics of calculated molecules were studied and compared with corresponding experimental results.All the theoretical results agree well with the measurement.For 2-D molecule with two-fold symmetry,the dominant charge transfer is off-diagonal,while for three-fold symmetry 2-D molecule,the dominant charge transfer is not only between branches and central group but also among branches.     

Influences of the molecule–electrode interface structure on the conducting characteristics of the gold-4,4 bipyridine-gold molecular junction

Two popular models of the gold-4,4 bipyridine (44BPD)-gold molecular junction, i.e., the direct contact of the 44BPD molecule with the Au(1 1 1) surface and the intermediary contact through one extra gold atom on each side, were studied using density functional theory calculations under periodic boundary conditions. The relative position of the Fermi level is changed by the extra gold atom from well below the LUMO (lowest unoccupied molecular orbital) of the 44BPD molecule in the direct contact model to within the energy range of the LUMO in the intermediary contact model, indicating that the local structure of the contact can significantly affect the conducting characteristics of the junction. The dependence of the molecule–electrode interaction on the interface structure was also investigated in details.     

Adsorption energies of molecular oxygen on Au clusters

The adsorption properties of O(2) molecules on anionic, cationic, and neutral Au(n) clusters (n=1-6) are studied using the density functional theory (DFT) with the generalized gradient approximation (GGA), and with the hybrid functional. The results show that the GGA calculations with the PW91 functional systemically overestimate the adsorption energy by 0.2-0.4 eV than the DFT ones with the hybrid functional, resulting in the failure of GGA with the PW91 functional for predicting the adsorption behavior of molecular oxygen on Au clusters. Our DFT calculations with the hybrid functional give the same adsorption behavior of molecular oxygen on Au cluster anions and cations as the experimental measurements. For the neutral Au clusters, the hybrid DFT predicts that only Au(3) and Au(5) clusters can adsorb one O(2) molecule.