A computational study of oxygen-termination of a (6,0) boron nitride nanotube

Abstract  

We performed density functional theory (DFT) calculations to investigate the properties of electronic structures of representative armchair and zigzag silicon carbide nanotubes (SiCNTs). The model structures were optimized and the NMR parameters were calculated at the sites of silicon-29 and carbon-13 atoms in these structures. Our results indicated that different electronic environments could be detected by using the atoms of nanotubes in which the atoms of tips, especially for zigzag SiCNT, exhibit distinctive properties among other atoms.     

Armchair型石墨纳米带的电子结构和输运性质

利用第一性原理的电子结构和输运性质计算方法, 研究了扶手椅(armchair)型单层石墨纳米带(具有锯齿边缘)的电子结构和输运性质及其边缘空位缺陷效应. 研究发现, 完整边缘的扶手椅型石墨纳米带是典型的金属性纳米带, 边缘空位缺陷的存在对扶手椅型纳米带能带结构有一定的影响,但并不彻底改变其金属性特征.     

A density functional theory study of van der Waals interaction in carbon nanotubes

In this article, we investigate the effect of van der Waals force in zigzag carbon nanotubes (CNTs) including single-wall CNT (SWCNT) and double-walled CNT (DWCNT) structures with several interaction configurations. The solid-state density functional theory is employed to calculate the geometric optimization, normal mode frequencies, and IR and Raman spectra with the periodic boundary condition. For SWCNTs, we find that the Raman intensity is not affected by the tube diameter or the electronic structure. The IR absorption, however, increases with the tube diameter. We find that the close metallicity of the electronic structure has a significant impact on the IR simulations. When the van der Waals force is applied outside the CNTs at a distance longer than 3.0, the effect on Raman spectra is minimal but some effects can still be confirmed by IR absorption. When the van der Waals force acts inside the CNTs, the effect on the spectrum can be observed, especially at a distance of 2.8 Å, both IR and Raman can be significantly enhanced in many modes.     

Electronic structure of niobium-doped molybdenum disulfide nanotubes

The effect of doping transition metal disulfide nanotubes on their structural and electronic properties was studied for the first time using self-consistent band-structure calculations by the density functional tight-binding method (DFTB). The influence of partial Nb → Mo substitution in the walls of MoS₂ nanotubes of various diameters and atomic configurations (armchair and zigzag) on their electronic structure, structural parameters, and relative stability is exemplified by a series of “mixed” Mo_0.9Nb_0.1S₂ nanotubes. The electronic properties of Mo_0.9Nb_0.1S₂ nanotubes are discussed as a function of the possible types of distribution of doping Nb atoms in the tubes.     

Dynamics and density profile of water in nanotubes as one-dimensional fluid

The transport and structural properties of water confined in nanotubes with different diameters were studied by molecular dynamics (MD) simulation. The effects of pore size, molecule-wall interaction, and the helicity of CNT on the diffusivity, thermal conductivity, and shear viscosity as well as density profile were analyzed. For diffusivity, in model NT > in armchair CNT > in zigzag CNT at similar conditions. However in contrast to the diffusivity, the thermal conductivity and the shear viscosity increase as the pore size decreases, in zigzag CNT > in armchair CNT > (or approximately ) in model NT. The ordered layer distribution of water molecules in nanotubes is clear. It suggests the structure of fluid in the zigzag CNTs is more ordered, and more solidlike. In the nanotubes, where the molecule and the pore dimensions are of similar order of magnitude, the nature of water-water and water-wall interactions, the confinement effect of space, and the helicity of CNT become more significant.     

Structural and electronic characteristics of perhydrogenated carbon nanotubes

The structural and electronic characteristics of fully hydrogenated armchair and zigzag carbon nanotubes have been determined by quantum chemical methods. With use of line group symmetries, the structures of nanotubes up to 10 nm in diameter could be optimized by periodic B3LYP calculations. “In–out” isomerism is shown to significantly stabilize perhydrogenated carbon nanotubes, the energetically most favorable structures being those with 1/3–1/2 of the carbon atoms endo-hydrogenated. In favored nanotubes the ratio of endo- to exo-hydrogens is 1:1, the stabilities increasing as a function of the diameter of the nanotube. The calculated band gaps indicate that the perhydrogenated carbon nanotubes are insulators.     

Computational studies of carbon nanotube-hydrocarbon bond strengths at nanotube ends: effect of link heteroatom and hydrocarbon structure

Semiempirical and density functional electronic structure theory methods were used to study SWNT-X--R bond strengths, where the single-walled carbon nanotube (SWNT) had an armchair or zigzag structure, the link heteroatom X was O, N(H), or S and the hydrocarbon chain R was CH(2)CH(3), CH(OH)CH(3), CHCH(2), or CH(CF(3))CH(3). In all systems the hydrocarbon was bonded to the end of the nanotube. The SWNT-X--R bond (that is, the bond joining the link atom to the hydrocarbon) is more than 0.4 eV stronger for armchair than for zigzag nanotubes with the same diameters, irrespective of whether O, N, or S are used as link atoms or whether OH, C==C, or CF(3) groups are present in the hydrocarbon chain. This raises the possibility for selective manipulation of armchair/zigzag nanotubes using a variety of link atoms and hydrocarbon structures. The SWNT-O--CH(CF(3))CH(3) bond is weaker than the SWNT-O--CH(2)CH(3) bond (for both armchair and zigzag nanotubes), while inclusion of a double bond in the ethyl chain increases the bond strengths. Also, SWNT-S--CH(2)CH(3) and SWNT-N(H)--CH(2)CH(3) bonds are stronger than SWNT-O--CH(2)CH(3) bonds.     

Theoretical investigation of electromechanical effects for graphyne carbon nanotubes

We present a theoretical study of the electronic and mechanical properties of graphyne-based nanotubes (GNTs). These semiconducting nanotubes result from the elongation of one-third of the covalent interconnections of graphite-based nanotubes by the introduction of yne groups. The effect of charge injection on the dimensions of GNTs was investigated using tight-binding calculations. Low amounts of electron injection are predicted to cause qualitatively different responses for armchair and zigzag graphyne nanotubes. Although the behavior is qualitatively similar to the usual carbon nanotubes, the charge-induced strains are predicted to be smaller for the GNTs than for ordinary single walled carbon nanotubes.     

接枝羧基对单壁碳纳米管弹性性质的影响

采用分子动力学方法对端口接枝不同数量羧基的扶手椅型和锯齿型单壁碳纳米管弹性模量进行了模拟研究. 结果表明, 扶手椅型(5, 5)、(10, 10)管和锯齿型(9, 0)、(18, 0)管在未接枝状态下杨氏模量分别为948、901GPa和804、860 GPa. 在接枝2-8个羧基情况下, 扶手椅型单壁碳纳米管拉伸杨氏模量基本不随接枝数量的增加而发生变化, 而锯齿型单壁碳纳米管则不同, 接枝状态下的弹性模量比未接枝状态小很多, 但随接枝数量的增加又呈略增趋势. 分别从接枝后碳纳米管变形电子密度等值线结构变化、键长变化和系统势能变化规律等方面, 对单壁碳纳米管弹性模量的接枝效应进行了分析.     

SiC-doped boron nitride nanotubes: computations of 11B and 14N quadrupole coupling constants

Abstract  

Density-functional theory calculations have been performed to investigate the properties of the electronic structures of silicon–carbon-doped boron nitride nanotubes (BNNTs). The geometries of zigzag and armchair BNNTs were initially optimized and the quadrupole coupling constants subsequently calculated. The results indicate that doping of B and N atoms by C and Si atoms has more influence on the electronic structure of the BNNTs than does doping of B and N atoms by Si and C atoms. The changes of the electronic sites of the N atoms are also more significant than those of the B atoms.     

受限于不同螺旋性的纳米碳管中水的分子动力学模拟

近年来将纳米碱米碳管引入到与生命过程息息相关的离子通道膜的研究逐渐成 为热点，而其中的关键就是要了解受限于膜孔道（碳管）中水分子的行为。采用分 子动力学模拟在300 K和1.01 * 10~5 Pa下对受限于（6，6）armchair型和（10， 0）zigzag型纳米碳管中的水进行了研究，得到了水分子在碳管中的局部密度分布 等静态性质以及水分子在碳管中的传递等动态性质，并对不同势能模型的模拟结果 作了比较。结果表明选择不同的势能模型并没有改变此体系的固有性质，即水分子 不仅能够进入到憎水性的（6，6）碳管中而且能形成一条稳定的由氢键相连的纵列 （single file），而且在管中以纵列的形式进行同歇传递。此外，碳管螺旋性对 受限水的静态性质影响不大但对动态性质则有一定程度的影响，水分子在（10，0 ）zigzag型碳管中的传递能力要强于在（6，6）armchair型碳管中的能力。     

The effect of 3d-metal intercalation on the electronic structure of metallic and semiconducting nanotubes

The electronic structure of 3d-metal-intercalated metallic (5,5) and semiconducting (10,0) nanotubes has been studied by quantum-chemical methods. The total and partial densities of states of nanotubes as a function of metal concentration and nature and the carbon-shell structure have been calculated by the linear augmented-cylindrical-wave method. Metalized nanowires based on armchair (5,5) and zigzag (10,0) nanotubes with one, two, three, and four metal atoms in the cross-section have been calculated. The introduction of the metal is accompanied by a sharp increase in the density of states at the Fermi level of the nanowire, which determines the concentration of free electrons involved in charge transfer in the nanotube. The 3d electrons of the metal and the carbon shell are nearly equally involved in electron transport in intercalated wires. Both the 3d electrons of a metal and the carbon shell should be nearly equally involved in electron transport in intercalated wires. The introduction of metals not only affects the conductive state of the carbon nanotube but also changes the entire pattern of its valence band, in particular, increases the valence band width of the nanotube by 5–10 eV owing to the low-energy shift of the 2s(C) states.     

接枝羟基对有限长碳纳米管电子结构的影响

基于局域密度泛函理论, 采用第一原理方法, 建立了(5, 5)型和(8, 0)型有限长碳纳米管的原子模型, 并在两个端口接枝1～8个羟基官能团, 先用DMol3中BLYP方法对其结构进行优化, 再利用CASTEP软件计算其电子分布和态密度的变化, 从而讨论羟基官能团对碳纳米管电子结构和电子输运特性的影响. 计算表明, 接枝羟基的碳纳米管的电子结构明显改变, 费米能级上的电子态密度下降, 最高占据轨道上电子的非定域程度减弱, 致使电子输运性能呈下降趋势.     

Computational studies of effects of tubular lengths on the NMR properties of pristine and carbon decorated boron phosphide nanotubes

Density functional theory (DFT) calculations were performed to investigate the effects of tubular lengths on the nuclear magnetic resonance (NMR) properties of boron phosphide (BP) nanotubes. To this aim, the properties of pristine and carbon decorated (C-decorated) models of representative zigzag and armchair BP nanotubes were investigated. The results indicated that the atoms at the edges of nanotubes do not detect any significant changes. The NMR properties of boron atoms only detect slight changes but those of phosphorous atoms are more notable.     

Ferromagnetism induced by intrinsic defects and boron substitution in single-wall SiC nanotubes

On the basis of density functional theory (DFT) methods, we study the magnetic properties and electronic structures of the armchair (4, 4) and zigzag (8, 0) single-wall SiC nanotubes with various vacancies and boron substitution. The calculation results indicate that a Si vacancy could induce the magnetic moments in both armchair (4, 4) and zigzag (8, 0) single-wall SiC nanotubes, which mainly arise from the p orbital of C atoms surrounding Si vacancy, leading to the ferromagnetic coupling. However, a C vacancy could only bring about the magnetic moment in armchair (4, 4) single-wall SiC nanotube, which mainly originates from the polarization of Si p electrons, leading to the antiferromagnetic coupling. In addition, for both kinds of single-wall SiC nanotubes, magnetic moments can be induced by a boron atom substituting for C atom. When two boron atoms locate nearest neighbored, both kinds of single-wall Si(C, B) nanotubes exhibit antiferromagnetic coupling.     

Prediction of the Frontier Electronic States in a Finite Single-wall Carbon Nanotube

A theoretical model is summarized into the shorter vector principle. It is used to predict the topological structure of wave function and the oscillation rule of energy gap in various types of finite carbon nanotubes (CNTs). The theoretical model indicates that the characteristics of the electronic states only depend on the nanotube size and its symmetry along the shorter vector direction. In this direction, the wave functions of the original 3m (or 3m/2) periodicity are also suitable for armchair, chiral and zigzag finite CNTs with the C2 (Cs), C1 and Cn point groups, respectively. Energy gaps present the oscillation with 3m (or 3m/2) or odd-even n. The first principle calculations for some prototype systems are performed. The results are consistent with the theoretical model.     

Structure and electronic properties of deformed single-walled carbon nanotubes: quantum calculations

The electronic properties of single-walled carbon nanotubes (SWCNTs) can be modified by deforming their structure under high pressure. The aim of this study was to use quantum calculations to investigate one such property, the energy band gap, in relation to molecular structures of armchair and zigzag SWCNTs of various sizes and shapes deformed by applied forces. To model the increase in pressure, the degree of flatness (η) of the SWCNTs was adjusted as the primary parameter. The calculations gave accurate C-C bond lengths of the SWCNTs in their distorted states; these distortions significantly affected the electronic properties, especially the energy band gap of the SWCNTs. These results may contribute to a more refined design of new nano-electronic devices.     

Theoretical study of the 13C NMR spectroscopy of single-walled carbon nanotubes

The 13C NMR spectroscopy of armchair and zigzag single-walled carbon nanotubes has been investigated theoretically. Spectra for (4,4), (5,5), (6,6), (6,0), (9,0), and (10,0) nanotubes have been simulated based on ab initio calculations of model systems. The calculations predict a dominant band arising from the carbon atoms in the "tube" with smaller peaks at higher chemical shifts arising from the carbon atoms of the caps. The dominant band lies in the range of 128 and 138 ppm. Its position depends weakly on the length, width, and chirality of the tubes. The calculations demonstrate how structural information may be gleaned from relatively low-resolution nanotube 13C NMR spectra.     

Interaction of a transition metal atom with intrinsic defects in single-walled carbon nanotubes

Interaction of a transition metal atom with defects in single-walled carbon nanotubes (SWNTs) were investigated through density functional theory calculations. For three kinds of intrinsic defects (single vacancies, double vacancies and Stone-Wales defects) in (5,5) armchair and (10,0) zigzag SWNTs, stable configurations were analyzed. The orientation of the specific bonds of the defects is related to the most stable configuration among several possible configurations. The stable adsorption sites and binding energies of a Ni atom on three intrinsic defects were calculated and compared to those on perfect side walls. All defects enhance Ni adsorption, and the single vacancy shows the most exothermic binding. These results shed light on the nature of the interaction of the transition metal with defects in SWNT, an important topic to the many aspects of carbon nanotubes interacting with transition metals. Particularly, this is useful for the fabrication of nanosized transition metal particles supported on carbon nanotubes.