1,8-二巯基芘分子电学特性的理论研究

在第一性原理的基础上 ,对 1,8 二巯基芘分子的电学特性进行了理论研究 .采用了 3个Au原子构成的团簇来模拟Au表面 .首先利用密度泛函理论计算了 1,8 二巯基芘分子的电子结构及其和Au表面的相互作用 ,再利用前线轨道理论和微扰理论定量地确定了该分子和Au表面的相互作用能常数 .最后利用弹性散射格林函数法研究了该分子结的伏 安特性 .计算结果表明 ,分子中的硫原子和Au原子形成很强的共价键 .当外加偏压小于 1V时分子结存在电流禁区 ,随着偏压升高 ,分子结的电导出现平台结构 .分子结的电导特性和其电子结构密切相关 ,扩展分子轨道为电荷的迁移提供了通道 ,而局域轨道对电流贡献很小     

分子和金表面相互作用的第一性原理研究

硫氢官能团可以很强地吸附于金表面上,从而可作为连接体用于纳米电子学中的分子器件.从第一性原理出发利用密度泛函理论研究了4,4′二巯基联苯分子和金表面的相互作用,并利用了前线轨道理论和微扰理论定量地确定了该相互作用能常数.计算结果表明,当含有硫氢官能团的有机分子化学吸附于金表面时,硫原子将与金原子形成以共价键为主的混和键,此时一些分子轨道扩展于金原子和有机分子中,这些轨道为分子结中电子的输运提供了通道,从而可使分子线的电导呈现出欧姆特性.而其他分子轨道具有局域性,此时电子的输运只能通过隧道效应来实现. 关键词： 化学吸附 分子线 分子电子学     

分子线的电子输运特性

从第一性原理出发利用密度泛函理论计算了共扼分子2氨基5硝基1,4二乙炔基4′苯硫醇基苯(2amino5nitro1,4diethyny4′benzenethiolbenzene)的电子结构,并利用前线轨道理论和微扰理论定量地确定了该分子与金表面的相互作用能常数.然后,利用弹性散射格林函数方法研究了该分子与金表面形成的分子线的伏安特性.计算结果表明,分子通过硫氢官能团可以很强地吸附于金表面上,形成以共价键为主的混合键,从而为电子的转移提供了通道.当外加偏压很低时,分子线的电流存在禁区,禁区的宽度约08eV. 关键词： 化学吸附 分子线 分子电子学     

分子线的伏-安特性研究

利用密度泛函理论计算了共扼分子2-氨基-5-硝基-1, 4-二乙炔基-4′-苯硫醇基苯的电子结构, 并利用弹性散射格林函数方法研究了该分子与金表面形成的分子线的伏-安特性. 该工作将有利于未来分子电子学器件的设计.     

分子结电学特性的理论研究

在第一性原理的基础上，对共扼分子2-氨基-5-硝基-1，4-二乙炔基-4’，-苯硫醇基苯(2-amino-5-nitro-1,4-diethyny-4’-benzenethiol-benzene)与金表面形成的分子结的电学特性进行了理论研究.利用密度泛函理论计算了该分子及扩展分子的电子结构；讨论了分子与金表面的相互作用，定量地确定了耦合常数，求出了电子的迁移强度；利用弹性散射格林函数法研究了该分子结的伏—安特性.计算结果表明，当外加偏压小于0.9V时分子结存在电流禁区，随着偏压升高，分子结的电导出现平台特 关键词： 化学吸附 分子结 分子电子学     

六元杂环分子电学特性的理论研究

在第一性原理基础上，利用弹性散射格林函数方法，研究了六元杂环分子结2,5-哒嗪二硫酚 、2,5-吡嗪二硫酚和2,5-嘧啶二硫酚的电子输运特性，分析了终端原子的选取对杂环分子吡 啶电学特性的影响. 利用分子前线轨道理论和微扰方法定量地确定了分子与金属的相互作用 能参数. 计算结果表明，2,5-哒嗪二硫酚具有较好的电学特性，而2,5-嘧啶二硫酚在外加电 压较低时电导值比较小. 对于吡啶分子，选取硒原子作为终端原子时，其导电特性优于分别 以氧原子和硫原子作为终端原子的情况. 关键词： 六元杂环分子 伏安特性 电子输运 分子电子学     

光致异构体开关特性的理论研究

利用弹性散射格林函数方法,对4,4-二羧基1,2-二苯乙烯分子的两种异构体与金电极构成的单分子结进行了研究. 研究表明,该类分子是通过末端羧基化学吸附于金表面的,两种分子结电导特性的差异主要是因为分子与电极的相互作用所致. 对每一种分子来说,都存在三种不同的稳定电导值,分别对应着分子末端与金表面的不同接触方式. 分子与金表面的相互作用导致分子结电子结构的变化是其电导差异的主要原因. 理论结果与实验测量结果符合得较好. 关键词： 光致异构体 伏安特性 电子输运 分子电子学     

1,4-丁二硫醇分子器件电输运性质的力敏特性研究

基于杂化密度泛函理论,研究了1,4-丁二硫醇分子体系的结构随电极作用力的变化及拉断过程;并利用弹性散射格林函数方法进一步计算了不同电极作用力下分子体系的电输运特性.结果显示,界面结构不同,拉断分子体系所用的拉力也不同:分子末端硫原子处于Au(111)面的空位上方时,拉断分子体系需约1.75 nN的拉力;若金电极表面存在孤立金原子与1,4-丁二硫醇分子末端的硫原子相连,拉断分子体系只需约1.0 nN的力,且伴有孤立金原子被拉出.两种情况分别与不同实验测量相符合.分子在压缩过程中发生扭曲并引起表面金原子滑移,然而压缩扭曲过程与拉伸回复过程不可逆.电极拉力约为0.7—0.8 nN时,分子体系在不同界面构型下以及在不同扭转状态下,电导都出现极小值,这与实验结论一致.分子的末端原子与电极间耦合强度随电极作用力的变化是引起分子体系电导变化的主要因素.实验在0.8 nN附近同时测得较小概率的高电导值与双分子导电有关.     

4 ,4′-二巯基二苯醚分子的电子输运性质研究

利用从头算方法和弹性散射格林函数理论,研究了4 ,4′-二巯基二苯醚分子的电输运性质.计算表明,当外加偏压少于0 .9 V时,该分子器件不导电.当外加偏压进一步增加时,该分子器件的电导呈现出平台特征.由于中间氧原子的存在,相对于4 ,4′-二巯基联苯分子来说,该分子的导电特性较差.     

同分异构体分子器件的电输运特性

利用从头算理论和弹性散射格林函数的方法,计算杂环分子体系同分异构体的电导和电流.结果表明,扩展分子轨道和耦合系数是影响分子体系电输运特性的两个重要因素.各同分异构体中氮原子位置和终端原子的不同,使其分子轨道的扩展性和与电极的耦合程度存在差别,导致其电输运特性的差异.     

First-principle studies of I–V properties of a molecular wire

The elastic scattering Green function method has been developed to describe the I–V characteristics of molecular wires. The molecular electronic structure and the interaction between the molecule and the gold surface are two key factors for the charge transport properties of molecular wires in the formulas. Anab initio calculation at the hybrid density functional theory level is carried out to obtain the electronic structure of 4-4′-dimercaptodibenzene molecule. The frontier orbit theory and the perturbation theory are employed to determine the constant of the interaction energy between molecule and surface quantitatively. The numerical results show that the bonding between the sulfur atom and the gold atoms corresponds mainly to the covalent bond. Some molecular orbits are extended over molecule and gold cluster that certainly give channels for the charge transport, other molecular orbits are localized and the charge transport can take place by tunnel mechanism. At zero bias region, there exists a current gap. With the increasing bias, the conductance of the wire takes a shape of plateaus.     

First-principle studies of I-V properties of a molecular wire

The elastic scattering Green function method has been developed to describe the I-V characteristics of molecular wires. The molecular electronic structure and the interaction between the molecule and the gold surface are two key factors for the charge transport properties of molecular wires in the formulas. An ab initio calculation at the hybrid density functional theory level is carried out to obtain the electronic structure of 4-4′-dimercaptodibenzene molecule. The frontier orbit theory and the perturbation theory are employed to determine the constant of the interaction energy between molecule and surface quantitatively. The numerical results show that the bonding between the sulfur atom and the gold atoms corresponds mainly to the covalent bond. Some molecular orbits are extended over molecule and gold cluster that certainly give channels for the charge transport, other molecular orbits are localized and the charge transport can take place by tunnel mechanism. At zero bias region, there exists a current gap. With the increasing bias, the conductance of the wire takes a shape of plateaus.     

电场对分子线电子结构的影响

从第一性原理出发,利用密度泛函理论计算了分子2-氨基-5-硝基-1,4-二乙炔基-4-苯硫醇基苯与金原子团形成的分子线的电子结构,从轨道、能级及吸附电子三个方面讨论了电场对分子线电子结构的影响.该工作将有利于未来纳米电子学器件的设计.     

分子和金表面相互作用的第一性原理研究

从第一性原理出发利用密度泛函理论研究了 4 ,4′ 二巯基联苯分子和金表面的相互作用 ,并利用了前线轨道理论和微扰理论定量地确定了该相互作用能常数. By using density functional theory, we have investigated the interaction between a thiol-phenyl molecule (4-4′-dimercaptodibenzene) and a gold surface. The frontier orbit theory and the perturbation theory are also employed to determine quantitatively the constant of interaction energy. The results show that the bonding between the sulfur atom and the gold atoms corresponds mainly to the covalent bond and some molecular orbits are extended over the molecule and gold cluster which certainly give channels...     

Electronic Transport Calculations Using Maximally-Localized Wannier Functions

I present a method to calculate the ballistic transport properties of atomic-scale structures under bias. The electronic structure of the system is calculated using the Kohn-Sham scheme of density functional theory (DFT). The DFT eigenvectors are then transformed into a set of maximally localized Wannier functions (MLWFs) [N. Marzari and D. Vanderbilt, Phys. Rev. B 56 (1997) 12847]. The MLWFs are used as a minimal basis set to obtain the Hamitonian matrices of the scattering region and the adjacent leads,which are needed for transport calculation using the nonequilibrium Green's function formalism. The coupling of the scattering region to the semi-infinite leads is described by the self-energies of the leads. Using the nonequilibrium Green's function method, one calculates self-consistently the charge distribution of the system under bias and evaluates the transmission and current through the system. To solve the Poisson equation within the scheme of MLWFs I introduce a computationally efficient method. The method is applied to a molecular hydrogen contact in two transition metal monatomic wires (Cu and Pt). It is found that for Pt the I-V characteristics is approximately linear dependence, however, for Cu the I-V characteristics manifests a linear dependence at low bias voltages and exhibits apparent nonlinearity at higher bias voltages. I have also calculated the transmission in the zero bias voltage limit for a single CO molecule adsorbed on Cu and Pt monatomic wires. While a chemical scissor effect occurs for the Cu monatomic wire with an adsorbed CO molecule, it is absent for the Pt monatomic wire due to the contribution of d-orbitals at the Fermi energy.     

Bias drop and phonon emission in molecular wires

Using the recursion-transfer-matrix (RTM) method combined with the non-equilibrium Green's function (NEGF) method and density-functional theory, we perform ab initio calculations for the electron transport of molecular wires bridged between electrodes. We present an effective potential of molecular wire under a finite bias voltage and discuss the phonon emission and local heating due to inelastic electron-phonon coupling effects. We find that it is strongly dependent on contact conditions. When the contacts to electrodes are bad, excitation phonon modes at contacts become dominant for the energy dissipation.     

Theoretical investigation on current–voltage characteristics in all-carbon molecular device with different contact geometries

Applying nonequilibrium Green's functions in combination with the first-principles density-functional theory, we investigate electronic transport properties of an all-carbon molecular device consisting of one phenalenyl molecule and two zigzag graphene nanoribbons. The results show that the electronic transport properties are strongly dependent on the contact geometry and device's currents can drop obviously when the connect sites change from second-nearest sites from the central atom of the molecule (S site) to third-nearest sites from the central atom of the molecule (T site). More importantly, the negative differential resistance behavior is only observed on the negative bias region when the molecule connects the graphene nanoribbons through two T sites.