Negative Differential Resistance in Atomic Carbon Chain-Graphene Junctions

We investigate the electronic transport properties of atomic carbon chain-graphene junctions by using the density-functional theory combining with the non-equilibrium Green's functions. The results show that the transport properties are sensitively dependent on the contact geometry of carbon chain. From the calculated I-V curve we find negative differential resistance (NDR) in the two types of junctions. The NDR can be considered as a result of molecular orbitals moving related to the bias window.     

First-principle study of the electronic transport properties of a new dumbbell-like carbon nanocomposite

Using a first-principle density functional theory and non-equilibrium Green's function formalism for quantum transport calculation, we have investigated the electronic transport properties of a new dumbbell-like carbon nanocomposite, in which one carbon nanotube segment is capped with two C₆₀ fullerenes. Our results show that the current–voltage curve reveals a highly nonlinear feature. A negative differential resistance (NDR) behavior is obtained at a very low bias, which is expected to be helpful for the development of low bias NDR-based molecular devices. Moreover, the carbon nanotube length and fullerene type can affect the NDR behavior strongly. The electronic transport is analyzed from the transmission spectra and the molecular projected self-consistent Hamiltonian states under different applied biases.     

Gate-controlled low-bias rectifying behaviors in BDC60 molecule

Using first-principles density functional theory and non-equilibrium Greenʼs function formalism for quantum transport calculation, we have investigated the effect of gate voltage on the electronic transport properties of BDC60-based molecular junction. The results show that the transport properties are strongly modulated by the applied gate voltage, and the current–voltage curve displays an obvious rectifying behavior at much low bias region. The mechanism for the rectifying behavior is analyzed by the bias-dependent transmission spectrum, projected density of states, spatial distribution of molecular projected self-consistent Hamiltonian orbitals and voltage drop over the junction.     

C20F20分子电子输运性质的第一性原理研究

利用第一性原理密度泛函理论和非平衡格林函数方法研究了C₂₀F₂₀分子的电子输运性质. 计算得到了C₂₀F₂₀分子的平衡电导为0385 G₀ 其I-V曲线表现出较好的线性特性. 在有限偏压范围内具有较稳定的电导值, 可以用于制备稳恒电阻分子器件. 关键词： 20F₂₀分子')" href="#">C₂₀F₂₀分子 电子输运 分子器件     

First-principles study of the electronic transport properties of a C131 -based molecular junction

Using first-principles density functional theory and the non-equilibrium Green’s function formalism, we have studied the electronic transport properties of the dumbbell-like fullerene dimer C₁₃₁-based molecular junction. Our results show that the current-voltage curve displays an obvious negative differential resistance phenomenon in a certain bias voltage range. The negative differential resistance behavior can be understood in terms of the evolution of the transmission spectrum and the projected density of states with applied bias voltage. The present findings could be helpful for the application of the C₁₃₁ molecule in the field of single molecular devices or nanometer electronics.     

分子线电子输运特性的第一性原理研究

从第一性原理出发 ,利用密度泛函理论研究了SH -C8H16-SH分子和金表面的相互作用 ,并利用分子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 ,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 .研究结果表明 ,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 ,扩展的分子轨道使分子线的电导呈现出欧姆特性 ,而对于局域的分子轨道 ,电子的输运只能通过隧道效应来实现 .对分子线伏 安特性的计算结果显示 ,在零偏压附近 ,存在一个电流禁区 ,随着偏压的增加 ,分子线的电导呈现出平台特征 .     

金电极下二元化合物氮化镓链结构演化和电导的从头计算

基于从头密度泛函理论结合非平衡格林函数方法，首次研究了二元化合物GaN链介于两个金电极之间的电子输运性质。模拟了Au-(GaN)2-Au节点断裂过程，计算了相应的结合能，获得了平衡态电导以及平衡态下节点的投影态密度。此外，计算了平衡态下节点在微小偏压下的电流和电导。结果发现，随着偏压增强，GaN分子链的电导也随之下降。最后给出的伏安特性曲线呈现一个非线性关系，表明节点具有类似半导体的特征。     

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.     

Negative differential resistance in the unsymmetrical C121-based molecular junction

Using first-principles density functional theory and non-equilibrium Green?s function formalism for quantum transport calculation, we have investigated the electronic transport properties of the unsymmetrical C₁₂₁-based molecular junction. Our results show that the current-voltage curve displays a negative differential resistance phenomenon in a certain bias voltage range. The mechanism for the negative differential resistance phenomenon is suggested. The present findings could be helpful for the application of the C₁₂₁ molecule in the field of single molecular devices or nanometer electronics.     

DFT-NEGF study of transport properties and NDR behavior in fused furan and thiophene dimmers

The nonequilibrium Green's function approach in combination with density-functional theory is used to perform quantum mechanical calculations of the electron transport properties of furan and thiophene dimmers. Both the molecular systems have two S-linker and translated into the Gold junction with (1 1 1) surfaces. The studied molecular junctions at zero bias voltage are HOMO-based junctions and currents through these systems are driven by hole transport. The current–voltage characteristics of the both studied molecular junctions illustrate that negative differential resistance (NDR) feature is observed over the bias voltage of 2.0 V. Higher conductivity of fused furan dimmer and NDR character have been explained by the monitoring of the transmission resonance peak across the bias window against varying bias voltages.     

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     

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.     

Ab initio calculation of transport properties in 1,3-diphenylpropynylidene based molecular device

Using an ab initio method based on non-equilibrium Green’s functions (NEGF) combined with density functional theory (DFT), a calculation of the transport properties of a single molecular junction based on 1,3-diphenylpropynylidene (PhC₃Ph) ‘radical-π-radical’ is performed. The obvious negative differential resistance (NDR), spin current polarisation (SCP) and dual-spin current rectification (SCR) effects in this device are obtained. The total current for magnetic parallel configuration (PC) is larger at first and then less than that for magnetic antiparallel configuration (APC) as the bias increases, which suggests the abnormal magnetoresistance (MR) effect and can be used as a molecular switch with two working voltages. The evolution of the spin-polarised transmission spectrums and the frontier molecular orbitals (MOs) with applied bias is used to explain the above interesting results. Our calculations may be helpful for designing multifunctional molecular spintronics devices in the future.     

Ab initio analysis of electron-phonon coupling in molecular devices

We report a first principles analysis of electron-phonon coupling in molecular devices under external bias voltage and during current flow. Our theory and computational framework are based on carrying out density functional theory within the Keldysh nonequilibrium Green's function formalism. Using a molecular tunnel junction of a 1,4-benzenedithiolate molecule contacted by two aluminum leads as an example, we analyze which molecular vibrational modes are most relevant to charge transport under nonequilibrium conditions. We find that the low-lying modes are most important. As a function of bias voltage, the electron-phonon coupling strength can change drastically while the vibrational spectrum changes at a few percent level.     

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.     

Transport properties of boron-doped single-walled silicon carbide nanotubes

The doped boron (B) atom in silicon carbide nanotube (SiCNT) can substitute carbon or silicon atom, forming two different structures. The transport properties of both B-doped SiCNT structures are investigated by the method combined non-equilibrium Green’s function with density functional theory (DFT). As the bias ranging from 0.8 to 1.0 V, the negative differential resistance (NDR) effect occurs, which is derived from the great difficulty for electrons tunneling from one electrode to another with the increasing of localization of molecular orbital. The high similar transport properties of both B-doped SiCNT indicate that boron is a suitable impurity for fabricating nano-scale SiCNT electronic devices.     

OPE molecular junction as a hydrogen gas sensor

Oligo(phenylene ethynylene) (OPE) molecular junction has been suggested as a H₂ molecule sensor based on calculations using the first principles of density–functional theory and non-equilibrium Green's function. The electronic transport properties of the OPE molecule between two Au electrodes with or without adsorbed H₂ molecules are investigated. Results show that the adsorbed H₂ molecule significantly changes the characteristics of the current–voltage curve of the OPE molecular junction. The pure OPE molecular junction exhibits a significant negative differential resistance, but this kind of phenomenon will disappear or weaken after hydrogen molecules are adsorbed. The conductance of the junction also obviously decreases in the bias range of [−0.4, 0.4] V after adsorbing H₂ molecules. These effects can be used to design a H₂ molecule sensor.     

Spin-polarized transport properties of a pyridinium-based molecular spintronics device

By applying a first-principles approach based on non-equilibrium Green's functions combined with density functional theory, the transport properties of a pyridinium-based “radical-π-radical” molecular spintronics device are investigated. The obvious negative differential resistance (NDR) and spin current polarization (SCP) effect, and abnormal magnetoresistance (MR) are obtained. Orbital reconstruction is responsible for novel transport properties such as that the MR increases with bias and then decreases and that the NDR being present for both parallel and antiparallel magnetization configurations, which may have future applications in the field of molecular spintronics.     

Nonlinear spin current and magnetoresistance of molecular tunnel junctions

We report on a theoretical study of spin-polarized quantum transport through a Ni-bezenedithiol(BDT)-Ni molecular magnetic tunnel junction (MTJ). Our study is based on carrying out density functional theory within the Keldysh nonequilibrium Green's function formalism, so that microscopic details of the molecular MTJ are taken into account from first principles. A magnetoresistance ratio of approximately 27% is found for the Ni-BDT-Ni MTJ which declines toward zero as bias voltage is increased. The spin currents are nonlinear functions of bias voltage, even changing sign at certain voltages due to specific features of the coupling between molecular states and magnetic leads.     

硼氮原子取代掺杂对分子器件负微分电阻效应的影响

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,研究了硼氮原子取代掺杂对三并苯分子电子输运性质的影响.计算结果表明,三并苯分子器件的电流在特定偏压区间内随电压的增加而减小呈现出负微分电阻效应,电流的峰谷之比高达5.12.用硼原子或者氮原子取代分子的中心原子后,器件0.8V以内的电流明显增加,但是负微分电阻效应减弱,相应的电流峰谷比分别降至3.83和3.61.分析认为,输运系数在特定偏压下的移动是器件负微分电阻效应的主要成因.核外电子数的差异导致硼氮原子掺杂取代可以使器件轨道及其透射峰分别向高能方向或者低能方向移动从而有效地调控了器件的低偏压下的电子传输能力和负微分电阻效应.