Tailoring atomic structure to control the electronic transport in zigzag graphene nanoribbon

We have performed ab initio   density functional theory calculation to study the electronic transport properties of the tailored zigzag-edged graphene nanoribbon (ZGNR) with particular electronic transport channels. Our results demonstrated that tailoring the atomic structure had significantly influenced the electronic transport of the defective nanostructures, and could lead to the metal-semiconducting transition when sufficient atoms are tailored. The asymmetric I–V$I\text{–}V$ characteristics as a result of symmetry breaking have been exhibited, which indicates the route to utilize GNR as a basic component for novel nanoelectronics.     

Electronic transport properties of silicon chains sandwiched between graphene electrodes: first-principles study

The effects of orientation and silicon chain length on the electronic transport properties for linear silicon chains sandwiched between two graphene electrodes are investigated by using non-equilibrium Green’s functions combined with density functional theory. Our results demonstrate that the conductance of single silicon chains can hardly be affected by its orientation, as there is negligible difference between the conductance of tilted and un-tilted chains, and the conductance is impacted greatly by the length of chains, i.e. the transmission coefficient is doubled for double chains. The equilibrium conductance of single silicon chains shows even-odd oscillating behavior, and its tendency decreases with the increase of the chain length. The non-equilibrium electronic transport properties for all types of chains are also calculated, and all current–voltage curves of silicon chains show a linear character. The frontier molecular orbitals, the total and projected density of states are used to analyse the electronic transport properties for all types of chains.     

A cytosine-assisted carbon nanotubes junction: DFT studies

Since nucleobase-functionalized carbon nanotubes (CNTs) are important in the biological applications; the junction of a pair of CNTs through a bridging cytosine linkage is investigated based on density functional theory (DFT) calculations. In the exact model of study, the CNTs are bound to N₁ and C₅ atomic sites of cytosine to make possible the CNT–cytosine–CNT model. To systematically investigate the purpose, the models of original CNT, original cytosine, and primary models of cytosine–CNT in which one CNT is only bound to N₁ or C₅ atomic site of cytosine are also considered. The results of dipole moments and binding energies indicated that the CNT–cytosine–CNT model is the most stable one among all three possible models cytosine-functionalized CNT. The values of energy gaps indicated that the conducting properties of primary cytosine–CNT models are not changed referring to the original CNT but better conductivity could be observed for the CNT–cytosine–CNT model. The values of evaluated quadrupole coupling constants indicated that the electronic densities of nitrogen and oxygen atoms of cytosine detect notable affects during the functionalization processes by the zigzag CNTs and the oxygen atom of CNT–cytosine–CNT model could be proposed as the most proper interacting site of cytosine among other functionalized zigzag models and also the original cytosine. However, the changes of quadrupole coupling constants for the atoms of cytosine are almost negligible during the functionalization processes by the armchair CNTs.     

First-principles study of C chemisorption and diffusion on the surface and in the subsurfaces of Ni(1 1 1) during the growth of carbon nanofibers

First-principles calculations based on density functional theory and the generalized gradient approximation have been used to study the C chemisorption and diffusion on the surface and in the subsurfaces of Ni(1 1 1). The threefold Hcp site is observed to be preferred by the C adsorption on Ni(1 1 1) surface while in the subsurfaces, the octahedral site is more energetically favorable than the tetrahedral site and all surface adsorption sites. The calculated binding energies have been compared with the previous experimental and theoretical results and good agreement is found. Minimum energy paths for the C diffusion between different adsorption sites are also investigated using the nudged elastic band method. It is predicted that if the C surface diffusion rate is higher than the production rate of C atoms during the growth of carbon nanofibers and the C concentration is low at the Ni surface, the generated C atoms are likely to diffuse on the catalyst surface predominantly because of the lowest energy barrier, while if the generated C production rate is higher and some adsorption sites are blocked by the accumulated carbon, the C atoms may diffuse both on the surface and in the subsurfaces simultaneously.     

Quantum walk transport on carbon nanotube structures

We study source-to-sink excitation transport on carbon nanotubes using the concept of quantum walks. In particular, we focus on transport properties of Grover coined quantum walks on ideal and percolation perturbed nanotubes with zig-zag and armchair chiralities. Using analytic and numerical methods we identify how geometric properties of nanotubes and different types of a sink altogether control the structure of trapped states and, as a result, the overall source-to-sink transport efficiency. It is shown that chirality of nanotubes splits behavior of the transport efficiency into a few typically well separated quantitative branches. Based on that we uncover interesting quantum transport phenomena, e.g. increasing the length of the tube can enhance the transport and the highest transport efficiency is achieved for the thinnest tube. We also demonstrate, that the transport efficiency of the quantum walk on ideal nanotubes may exhibit even oscillatory behavior dependent on length and chirality.     

铀碳氧系统分子结构的DFT计算

用密度泛函理论(DFT)的Bexke3lyp方法,对铀原子采用相对论有效原子实势及(6s5p2d4f)/[3s3p2d2f]收缩价基集合,碳、氧原子采用6-311G价基集合,应用Gaussian98程序对一氧化碳气体与铀表面相互作用的可能分子结构U-C-O、U-O-C、C-U-O(角形Cs和线形C∞v)等,进行abinitio优化计算.得到了十二种三重态或五重态的相对稳定结构的电子状态、几何构形、能量、谐振频率、力学性质和电性质等,并给出了角形和线形结构的正则振动分析图.结果表明,Cs构型的能量都比较低,尤其以U-C-O角形结构(3A″)为最低;通过对各成键原子间重叠布居数及键能分析知,U与CO的结合力较弱,O原子比C原子与U原子的结合力稍强.     

Time-dependent wave-packet approach to the quantum transport of carbon nanotubes with vacancies

We investigate the vacancy effect on the electronic transport properties of the (5,5)-metallic and (5,0)-semiconducting carbon nanotubes using the time-dependent wave-packet approach based on the Kubo-Greenwood formula within the tight-binding approximation. We found that the metallic and semiconducting carbon nanotubes show different electronic transport properties for the states created by vacancies.     

(InAs)1/(GaSb)1超晶格原子链的第一原理研究

利用第一原理平面波赝势法, 对(InAs)₁/(GaSb)₁超晶格原子链的原子结构、力学特性、电子能带结构、 声子结构和光学特性进行研究, 并结合密度泛函理论数值原子轨道赝势法和非平衡格林函数法计算量子输运特性. 与二维层结构的(InAs)₁/(GaSb)₁超晶格相比, (InAs)₁/(GaSb)₁超晶格原子链的能带结构有明显不同, 在某些情况下表现为金属能带特性. 对理想条件下(InAs)₁/(GaSb)₁ 超晶格原子链的力学强度计算表明, 该结构可承受的应变高达 ε=0.19. 通过对声子结构的完整布里渊区分析, 研究了(InAs)₁/(GaSb)₁超晶格原子链的结构稳定性. 对两端接触电极为Al纳米线的InAs/GaSb超晶格原子链的电子输运特性计算表明, 电导随链长和应变的改变而发生非单调变化.光吸收谱的计算结果表现出在红外波段具有陡峭吸收边, 截止波长随超晶格原子链的结构而变化.预计InAs/GaSb超晶格原子链可应用于红外光电子纳米器件, 通过改变超晶格原子链的结构来调节光电响应波段.     

Local probe of the interlayer coupling strength of few-layers SnSe by contact-resonance atomic force microscopy

The interlayer bonding in two-dimensional (2D) materials is particularly important because it is not only related to their physical and chemical stability but also affects their mechanical, thermal, electronic, optical, and other properties. To address this issue, we report the direct characterization of the interlayer bonding in 2D SnSe using contact-resonance atomic force microscopy (CR-AFM) in this study. Site-specific CR spectroscopy and CR force spectroscopy measurements are performed on both SnSe and its supporting SiO₂/Si substrate comparatively. Based on the cantilever and contact mechanic models, the contact stiffness and vertical Young’s modulus are evaluated in comparison with SiO₂/Si as a reference material. The interlayer bonding of SnSe is further analyzed in combination with the semi-analytical model and density functional theory calculations. The direct characterization of interlayer interactions using this non-destructive methodology of CR-AFM would facilitate a better understanding of the physical and chemical properties of 2D layered materials, specifically for interlayer intercalation and vertical heterostructures.     

钛原子位置对立方BaTiO3电子结构的影响

本文基于密度泛函理论(DFT)的第一原理方法,计算了Ti原子位置对BaTiO3电子结构的影响.Ti的位置变化导致晶格畸变,使电子结构发生变化;从能带结构、能态密度(DOS)、电子密度、Mulliken布居等计算结果分析表明,导带和价带主要由Ti的3d电子和O的2p电子,Ti原子位置的变化,使Ti的3d电子能量分布上移,而O的2p电子能量下移;Ti位置变化,Ti的3d电子与的sp电子形成的杂化轨道更趋向离子化,以致于使OI出现了正电荷,表明发生了的2p电子向Ti的转移;O原子电子的转移使得Ti原子在导带的3d电子能量降低,与O原子在价带的2p电子能量重叠,禁带消失;随着畸变程度提高,转移逐渐增强,使禁带宽度逐渐减小,直至完全消失.     

Thermoelectric performance of monolayer Bi2Te2Se of ultra low lattice thermal conductivity

The electronic structure and thermoelectric properties of monolayer Bi₂Te₂Se were studied by density functional theory and semi-classical Boltzmann transport equation. The band gap with TB-mBJ can be improved for monolayer Bi₂Te₂Se. Monolayer Bi₂Te₂Se have ultra-low thermal conductivity comparing with other well-known two-dimensional materials. The monolayer Bi₂Te₂Se can improve electrical conductivities. ZT increases with increasing temperature for monolayer Bi₂Te₂Se. Comparing to GGA, TB-mBJ has larger ZT value in p-type doping. Monolayer Bi₂Te₂Se have larger ZT comparing with other well-known two-dimensional materials. Our calculated results show that our calculation greatly underestimates ZT value, therefore, monolayer Bi₂Te₂Se should have a higher ZT value.     

A DFT studies of structural and quadrupole coupling constants properties in C-doped BeO nanotubes

In the framework of density functional theory (DFT), we calculated the electronic structures and the quadrupole coupling constants (CQ) in the pristine and carbon doped (C-doped) beryllium oxide nanotubes (BeONTs) for the first time. The pristine and C-doped forms of representative (10, 0) zigzag and (5, 5) armchair models of BeONTs were considered in this study. The structures are allowed to relax by performing all atomic optimization. Formation energies indicate that C-doping of Be atom (CBe form) could be more favorable than C-doping of O atom (CO form) in both zigzag and armchair BeONTs. Gap energies and dipole moments detected the effects of dopant in the (5, 5) armchair models; however, those parameters did not detect any significant changes in the C-doped (10, 0) zigzag BeONT models. The calculated nuclear quadrupole coupling constant for the Be and O nuclei reveal that the pristine models can be divided into layers of nuclei with an equivalent electrostatic environment such that those nuclei at the ends of tubes end up in a strong electrostatic environment when compared to the other nuclei along the length of tubes. Comparison with the available data on the pristine BeONTs reveals the influence of C-doping on the CQ parameters of Be and O atoms in the C-doped structures. For most lattice sites, the degree of influence on the CQ parameters of the zigzag model is larger than that of the armchair model. The calculations were performed based on the B3LYP DFT method and 6-31G^∗ standard basis sets using the Gaussian 09 program package.     

原子质量对一维三原子链色散关系的影响

本文采用数值分析方法研究原胞中原子质量对一维三原子链色散关系的影响,建立了频谱宽度和频率禁带宽度随原子质量变化的基本规律.结果表明,在原胞内只有一个原子质量发生变化的情况下,声学波频谱宽度随任一原子质量的增加而减小,光学波的频谱宽度随小原子质量的增加而增大,随大原子质量的增加而减小;两个频率禁带均随小原子质量的增加而变...     

The role of carbon impurities on the Si(0 0 1)-c(4 × 4) surface reconstruction: Theoretical calculations

In this work we employ the state-of-the-art pseudopotential method, within a generalized gradient approximation to the density functional theory, combined with a recently developed method for the calculation of HREELS spectra to study a series of different proposed models for carbon incorporation on the silicon (0 0 1) surface. A fully discussion on the geometry, energetics and specially the comparison between experimental and theoretical STM images and electron energy loss spectra indicate that the Si(1 0 0)-c(4 × 4) is probably induced by Si-C surface dimers, in agreement with recent experimental findings.     

First-principles study of palladium atom adsorption on the boron- or nitrogen-doped carbon nanotubes

We have performed first-principles calculation to investigate the adsorption of a single palladium atom on the surface of the pristine and boron- or nitrogen-doped carbon nanotubes (CNTs). The results show that for the adsorption of a single palladium atom on the pristine CNT surface, the most stable site is Bridge1 site above the axial carbon–carbon bond. Either boron- or nitrogen-doped CNTs can assist palladium surface adsorption, but the detailed mechanisms are different. The enhanced palladium adsorption on boron-doped CNT is attributed to the palladium d orbital strongly hybridized with both boron p orbital and carbon p orbital. The enhancement in palladium adsorption on nitrogen-doped CNT results from activating the nitrogen-neighboring carbon atoms due to the large electron affinity of nitrogen. Furthermore, the axial bond is preferred over the zigzag bond for a palladium atom adsorbed on the surface of all three types of CNTs. The most energetically favorable site for a palladium atom adsorbed on three types of CNTs is above the axial boron–carbon bond in boron-doped CNT. The enhancement in palladium adsorption is more significant for the boron-doped CNT than it is for nitrogen-doped CNT with a similar configuration. So we conclude that accordingly, the preferred adsorption site is determined by the competition between the electron affinity of doped and adsorbed atoms and preferred degree of the axial bond over the zigzag bond.     

The electronic transport properties for a single-wall ZnO nanotube with different coupling interfaces

The transport properties of a single-wall ZnO nanotube contacted with two Au (Al or Cu ) electrodes are investigated by a theoretical approach. Our results suggest the contact resistance for ZnO nanotube connected with Au electrodes is the largest one as compared with Al and Cu acting as electrodes. The local density of states (LDOS) near the ZnO nanotube/Cu(Al) interface shows the strong electronic interaction. Also shown is that for Au–ZnO system, we can observe a best rectifying performance, the next is the Al–ZnO system, and the third is Cu–ZnO system. This rectification is also fully rationalized by the calculated transmission spectra, the spatial distribution of the lowest unoccupied molecular orbital and highest occupied molecular orbital states, and the electrostatic potential distribution.     

CO adsorption on Cu(1 1 1) and Cu(0 0 1) surfaces: Improving site preference in DFT calculations

CO adsorption on Cu(1 1 1) and Cu(0 0 1) surfaces has been studied within ab initio density functional theory (DFT). The structural, vibrational and thermodynamic properties of the adsorbate–substrate complex have been calculated. Calculations within the generalized gradient approximation (GGA) predict adsorption in the threefold hollow on Cu(1 1 1) and in the bridge-site on Cu(0 0 1), instead of on-top as found experimentally. It is demonstrated that the correct site preference is achieved if the underestimation of the HOMO–LUMO gap of CO characteristic for DFT is corrected by applying a molecular DFT + U approach. The DFT + U approach also produces good agreement with the experimentally measured adsorption energies, while introducing only small changes in the calculated geometrical and vibrational properties further improving agreement with experiment which is fair already at the GGA level.     

ZnO原子链的结构稳定性和电子性质的第一性原理研究

本文采用基于密度泛函理论的第一性原理平面波赝势法,研究了ZnO原子链的结构稳定性和电子性质.结果表明：ZnO分子可以形成直线形结构、梯子形结构以及双梯子形结构等一维链式结构,而之字形链状结构是不能稳定存在的.计算结果也表明：这些稳定存在的一维原子链结构均表现出间接带隙的特征,而之字形结构的原子链却表现出了类似金属的能带特征. 关键词： 原子链 结构稳定性 电子结构 第一性原理计算