碳硅链和氮铝链的电子输运特性的第一性原理研究

采用第一性原理非平衡格林函数方法研究了一维碳硅链 （SiC）_n和氮铝（Al-N）_n的电子输运特性,n为原子链所包含的Si,C（Al,N）原子数目.碳硅链（SiC）_n（或氮铝链（Al-N）_n）置于两个Al（100）电极中.计算了一维碳硅链和氮铝链体系的平衡电导随原子链的长度变化情况.结果发现,它们的平衡电导随原子链的长度增加而减小.对电荷转移分析发现, 关键词： 平衡电导 分子开关 转移电荷     

电子关联效应对平行双量子点系统磁输运性质的影响

从理论上研究了平行双量子点系统中的电子关联效应对该系统磁输运性质的影响. 基于广义主方程方法, 计算了通过此系统的电流、微分电导和隧穿磁阻. 计算结果表明: 电子自旋关联效应可以促发一个很大的隧穿磁阻, 而电子库仑关联效应不仅可以压制电子自旋关联效应, 还可以导致负隧穿磁阻和负微分电导的出现. 对相关的基本物理问题进行了讨论.     

拓扑缺陷对Armchair型小管径多壁碳纳米管输运性质的影响

采用密度泛函理论和非平衡格林函数方法研究了纯净的及带有不同数目的Stone-Wale拓扑缺陷下的扶手椅型单壁, 双壁和三壁小管径碳纳米管的能带结构和电子输运性质, 通过计算并分析不同偏压下的微分电导和非弹性电子隧穿谱(IETS), 计算结果表明单壁, 双壁和三壁碳纳米管的特征偏压区间分别为[-1.0V, 1.0V], [-0.5V, 0.5V] 和[-0.25V, 0.25V], 特征偏压区间内SW拓扑缺陷所产生的电导波动平缓, 而特征偏压区间外因缺陷的数目变化所带来的电导波动显著, 通过IETS谱线的分析得到单壁, 双壁和三壁碳纳米管的特征峰偏压分别为 1.25V, 0.625V和 0.125V. 碳纳米管的特征偏压区间和IETS特征峰偏压可为较小管径碳纳米管单壁, 双壁和多壁类型的区分提供一种新的途径, 同时也为小管径多壁碳纳米管的输运性质在出现拓扑缺陷时的响应提供参考依据.     

拓扑缺陷对Armchair型小管径多壁碳纳米管输运性质的影响

采用密度泛函理论和非平衡格林函数方法研究了纯净的及带有不同数目的 Stone-Wale拓扑缺陷下的扶手椅型单壁,双壁和三壁小管径碳纳米管的能带结构和电子输运性质,通过计算并分析不同偏压下的微分电导和非弹性电子隧穿谱(IETS),计算结果表明单壁,双壁和三壁碳纳米管的特征偏压区间分别为[-1.0 V,1.0 V],[-0.5 V,0.5 V]和[-0.25 V,0.25 V],特征偏压区间内SW拓扑缺陷所产生的电导波动平缓,而特征偏压区间外因缺陷的数目变化所带来的电导波动显著,通过IETS谱线的分析得到单壁,双壁和三壁碳纳米管的特征峰偏压分别为±1.25 V,±0.625 V和±0.125 V.碳纳米管的特征偏压区间和IETS特征峰偏压可为较小管径碳纳米管单壁,双壁和多壁类型的区分提供一种新的途径,同时也为小管径多壁碳纳米管的输运性质在出现拓扑缺陷时的响应提供参考依据.     

Na掺杂对C20H20分子的电子输运性质影响

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Na@C₂₀H₂₀分子的电子输运性质. 计算结果显示它的I-V曲线在偏圧 V范围内表现出了较好的线性特性, 出现了明显的负微分电阻现象, 并得到其平衡电导为0.0101G₀. 通过与Li@C₂₀H₂₀分子对比分析, 发现掺杂Na不仅能提高C₂₀H₂₀分子的电子输运能力, 而且 关键词： 20H₂₀分子')" href="#">Na@C₂₀H₂₀分子 电子输运 负微分电阻     

Au-Si-Au结点电子输运性质的第一性原理计算

采用密度泛函理论和非平衡格林函数相结合的方法对Au(100)-Si-Au(100) 系统左侧对顶位、右侧对空位的纳米结点的电子输运性质进行了理论模拟计算, 结果得到纳米结点的电导随电极距离(d_z)增大而减小. 在d_z =9.72 Å时, 结点的结合能最低, 结构最稳定, 此时电导为1.227G₀ (G₀=2e²/h), 其电子输运通道主要是Si原子的p_x, p_y和 p_z轨道电子形成的最高占居轨道共振峰; 在外偏压下, 电流-电压曲线表现出线性特征; 随着外加正负电压的增大, 电导略有减小, 且表现出不对称性的变化. 关键词： 硅原子 电子输运 密度泛函理论 非平衡格林函数     

钽硅团簇电子输运性质的第一性原理研究

利用基于密度泛函理论和非平衡格林函数的第一性原理方法,对位于两段半无限长铝导线之间的TaSi₃团簇的电子输运性质进行了研究.研究表明：该团簇分子投影自洽哈密顿量的8态和9态决定着系统在小偏压下的输运特性.TaSi₃团簇的平衡态电导对团簇与电极间距离的变化十分敏感,当距离小于0.35 nm时,平衡态电导随之剧烈的振荡;当距离大于0.35 nm后,平衡态电导迅速减小.在-1—1 V偏压下,团簇表现出一定的电压-电流非对称整流特性,在0.3—0.4 V的偏压下,观察到了该团簇的负微分电导特性. 关键词： 铝/钽硅混合团簇/铝分子结 电子输运 密度泛函理论 非平衡格林函数     

分子结点电子输运性质的理论研究

采用基于密度泛函理论的非平衡态格林函数方法,研究了Pt-H₂微结点在平衡态和低偏压下的电子输运行为,考察了电极-分子耦合形貌对结点输运性质的影响,并采用费曼路径概念从结点局域轨道出发分析了其输运特性. 发现H₂分子的反键轨道可以参与结点的低偏压电子输运,偏压可以通过改变系统局域分子轨道来影响其输运性质. 关键词： 分子结点 电子输运 非平衡态格林函数方法 透射谱     

电极位置和截面尺寸对分子器件输运性质的调控

研究表明分子器件的性能受器件结构搭建精度影响,分子与电极接触构型的微弱变化可能引起电输运特性较大差异.本文运用密度泛函理论和非平衡格林函数相结合的方法,研究了由金纳米线与benzene-1,4-dithiol（BDT）形成的分子结的电输运性质.通过对不同的Au-BDT接触构型输运性质的研究,发现当两电极处于对位构型时,有较好的电荷输运行为,而且比较符合制备工艺要求;当电极偏离轴线的角度不大于5°,且电极散射截面尺寸不小于4×4时,该分子结体系的电导和透射谱均比较稳定.电极截面尺寸小于4×4或者电极偏离轴线的夹角大于5°时,透射谱在费米能级附近出现不连续现象,导致体系电导降低.较小电极截面尺寸或者电极以较大角度偏离轴线将导致该分子结体系电导降低和透射谱连续性降低,主要是组成电极的金原子轨道与苯基分子轨道耦合缺失造成的.该研究为Au-BDT-Au体系设计和制备过程中电极的位置及电极截面尺寸做了科学的界定.     

有机分子结构对其电输运性质的影响

利用从头算理论和弹性散射格林甬数的方法,对有机分子1,4.苯二硫酚(benzene-1,4-dithiol)、4,4二巯基联苯(4,4-biphenyldithiol)、4,4:二巯基联苯醚(bis-(4-mercaptonphenyl)-ether)以及对苯二甲氰(1,4-phenylene diisocy-anide)的电子输运性质进行了理论研究和比较分析.结果显示前三种巯基分子在开启电压位置、电导的平台效应和电流的线性响应等方面有相似性,其中1,4-苯二硫酚分子的电输运性能优越于其他两个分子,但氰基分子对苯二甲氰却有较明显的区别.     

First principles investigation of the spin transport properties in graphene-porphine-graphene nanojunctions

The spin-dependent transport properties of a porphine molecule linking with two zigzag-edged graphene nanoribbon (ZGNR) electrodes have been investigated by using the density of functional theory (DFT) combined with the non-equilibrium Green’s function (NEGF) method. The device shows clearly negative differential resistance (NDR), large tunnelling magnetoresistance (TMR) of 10³ magnitude and nearly 100% perfect spin filter efficiency (SFE) properties, respectively. What’s more, the projected density of states (PDOS), molecular projected self-consistent Hamiltonian (MPSH) eigenvalues and transmission eigenstates were carried out to discuss the transport properties of the ZGNR/Porphine/ZGNR nanojunction. These results suggest that the ZGNR/Porphine/ZGNR device is a promising candidate for multi-functional spintronic devices.     

(CH3)2和(NH2)2基团修饰的齐聚苯乙炔分子电子输运性质研究

采用密度泛函理论和非平衡格林函数相结合的方法研究了S原子作为单、双端基的(CH₃)₂-OPE (齐聚苯乙炔)和(NH₂)₂-OPE分子在金电极间的电子输运性质. 通过第一性原理优化计算获得分子部分稳定结构, 再置于Au电极之间构成两极系统, 然后再优化整个两极系统获得稳定结构. 另外, 通过非平衡格林函数方法计算了两极系统的电子输运性质. 计算结果表明, 不同的修饰基团和桥接方式可以导致两极系统的开关效应、负微分电阻行为和整流行为等不同的电子输运性质. 通过计算不同偏压下的分子体系投影轨道电子分布、透射谱、态密度, 对这些新异的电输运性质出现的机理进行了解释.     

Spectroscopically determined potential energy surfaces of the H2O, H2O, and H2O isotopologues of water

Adiabatic potential energy surfaces (PESs) for three major isotopologues of water, H₂¹⁶O, H₂¹⁷O, and H₂¹⁸O, are constructed by fitting to observed vibration-rotation energy levels of the system using the nuclear motion program DVR3D employing an exact kinetic energy operator. Extensive tests show that the mass-dependent ab initio surfaces due to Polyansky et al. [O.L. Polyansky, A.G. Császár, S.V. Shirin, N.F. Zobov, P. Barletta, J. Tennyson, D.W. Schwenke, P.J. Knowles, Science 299 (2003) 539-542.] provide an excellent starting point for the fits. The refinements are performed using a mass-independent morphing function, which smoothly distorts the original adiabatic ab initio PESs. The best overall fit is based on 1788 experimental energy levels with the rotational quantum number J = 0, 2, and 5. It reproduces these levels with a standard deviation of 0.079 cm⁻¹ and gives, when explicit allowance is made for nonadiabatic rotational effects, excellent predictions for levels up to J = 40. Theoretical linelists for all three isotopologues of water involved in the PES construction were calculated up to 26 000 cm⁻¹ with energy levels up to J = 10. These linelists should make an excellent starting point for spectroscopic modelling and analysis.     

Microwave study of the submillimeter spectrum of the H2O?HF dimer

The study of the rotational spectrum of the H₂O?HF dimer in the equilibrium gas phase in the range 180-350 GHz by continuously frequency scanning microwave spectrometer with backward-wave oscillator and acoustic detection of absorption is described. The results of analyzing of the most intense spectral series are given. The assignment of some spectral series observed earlier is corrected. Data on the Coriolis interaction between the ground and excited vibrational states are obtained and spectroscopic constants of the dimer are significantly refined.     

Collisional broadening and shifting of the 211-202 transition of H2O, H2O, H2O by atmosphere gases

Broadening and shifting of the 2₁₁-2₀₂ transition of H₂¹⁶O, H₂¹⁷O, H₂¹⁸O by pressure of water, nitrogen and oxygen were precisely measured at room temperature using spectrometer with radio-acoustic detection of absorption. Shift parameters for all studied lines as well as broadening parameters of H₂¹⁷O, H₂¹⁸O lines were measured for the first time. Comparison of obtained results with previously known experimental and theoretical data is presented.     

Geometrical structures,vibrational frequencies,force constants and dissociation energies of isotopic water molecules （H2O,HDO, D2O,HTO, DTO,and T2O） under dipole electric field

The dissociation limits of isotopic water molecules are derived for the ground state. The equilibrium geometries, the vibrational frequencies, the force constants and the dissociation energies for the ground states of all isotopic water molecules under the dipole electric fields from -0.05 a.u. to 0.05 a.u. are calculated using B3P86/6-311++G(3df,3pf). The results show that when the dipole electric fields change from -0.05 a.u. to 0.05 a.u., the bond length of H-O increases whereas the bond angle of H-O-H decreases because of the charge transfer induced by the applied dipole electric field. The vibrational frequencies and the force constants of isotopic water molecules change under the influence of the strong external torque. The dissociation energies increase when the dipole electric fields change from -0.05 a.u. to 0.05 a.u. and the increased dissociation energies are in the order of H2O, HDO, HTO, D2O, DTO, and T2O under the same external electric fields.     

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.     

Collisional parameters of H2O lines: Velocity effects on the line-shape

This paper is devoted to the effects of velocity on the shapes of six R(J) lines of the ν₃ band of water vapor diluted in N₂. The experiments have been made at room temperature for total pressures between 0.1 and 1.2 atm using a tunable infrared laser frequency difference spectrometer. These measurements, which study broad and narrow lines of low and high J values, are first analyzed using the Voigt and the hard collision (HC) model. It is shown that both lead to unsatisfactory results, the Voigt profile being unable to account for the line narrowing whereas the friction (narrowing) parameter deduced using the HC approach has an unphysical dependence on pressure. Furthermore, at elevated pressure where Dicke narrowing and Doppler effects are negligible, deviations between experimental and fitted profiles are still observed, indicating inhomogeneous effects due to the speed dependence of collisional parameters. In order to go further, an approach based on the kinetic impact equation accounting for both the Dicke narrowing and the speed dependence has been applied. It uses velocity-dependent broadening and shifting coefficients calculated with a semi-classical approach and two parameters. The latter, which govern the memory functions of the modulus and orientation of the H₂O velocity are considered as free parameters and determined from experiments. The results show that all profiles, regardless of pressure and of the transition, can be correctly modeled using a single set of memory parameters. This demonstrates the consistency of the approach, which is then used to analyze the different regimes that monitor velocity effects on the line profile.     

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.