The interaction of Cr(CO)3 on the (n, 0) nanotube side-walls: a density functional study through a cluster model approach

Density functional calculations have been performed to investigate the functionalization of single-wall carbon nanotubes (SWNTs) with the Cr(CO)₃ metal fragment, employing extended molecular models. A circumcoronene molecule (C₅₄H₁₈), made by the fusion of 19 hexagonal carbon rings, can be regarded as a fragment of a graphene sheet. To reproduce the curvature of the SWNT surface, suitable geometric constraints have been imposed on the C₅₄H₁₈ model, freezing the positions of the outer hydrogens along the directions of the nanotube C-C bonds. Geometry optimizations have then been performed under this constraint on the Cr(CO)₃-C₅₄H₁₈ complexes, pointing out the most favourable coordination sites on the hexagonal rings of the carbon atom surface and the electronic properties of the resulting system. The effect of the curvature on the metal coordination to nanotubes has been analysed by investigating the interaction of the Cr(CO)₃ metal complex with the C₅₄H₁₈ molecules, modelling (n, 0) nanotubes with different degrees of curvature, i.e. with various values of the chiral vector (n, 0).     

Transport properties and mechanism of C60 coupled to carbon nanotube electrode

By applying non-equilibrium Green's functions in combination with density-functional theory, we investigate electronic transport properties of C₆₀ coupled to carbon nanotubes and Li electrodes. The results show that electronic transport properties of CNT-C₆₀-CNT and Li-C₆₀-Li systems are completely different. Nonlinear I-V characteristic, varistor-type behavior and negative differential resistance (NDR) phenomenon are observed when electrodes are carbon nanotubes. We discuss the mechanism of I-V characteristics of CNT-C₆₀-CNT systems in details. Our results suggest conductance, energy level of Frontier molecular orbitals, energy gap between HOMO and LUMO, the coupling between molecular orbitals and electrodes are all playing critical roles in electronic transport properties.     

富勒烯C20分子器件的电子结构和传导特性

运用基于密度泛函理论和基于非平衡格林函数的第一性原理方法研究了富勒烯C₂₀分子及连接电极构成的C₂₀分子器件的电子结构及电子输运性质.构建了三个基于C₂₀分子的嵌入K和Si原子的电子输运系统,并得到了电子透射谱和分子轨道分布.分析了三种器件的电子结构和输运性质的产生原因,说明C₂₀分子器件的电子传导主要集中在外壳.在C₂₀分子空笼中嵌入K和Si原子后,其电子输运仍然主要集中于富勒烯C₂₀的外壳. 关键词： 20分子')" href="#">富勒烯C₂₀分子 电子结构 电子传导     

A study of carbon nanosystems using the Hubbard model

The Hubbard model is used as a framework for analyzing carbon nanosystems: the fullerenes C₆₀ and C₈₀ and open-ended carbon nanotubes with chiralities (5, 5) and (10, 10) of various lengths. In the strong-correlation limit, the model predicts that open carbon nanotubes have a lower energy per atom as compared to C₆₀ and C₈₀ fullerenes. This finding contradicts the conventional view that dangling bonds increase the energy of a system. However, the increase, if any, is due to the presence of five-member carbon rings in fullerenes. The energy per atom should be higher for the five-member carbon ring compared to the six-member one, because the former cannot exist in a lower energy singlet state. Carbon nanotube growth is explained. The ionization energies and electron affinities of C₆₀ and C₈₀ fullerenes are calculated and found to agree well with experimental data.     

Electronic Transport in Molecular Junction Based on C20 Cages

Choosing closed-ended armchair （5, 5） single-wall carbon nanotubes （CCNTs） as electrodes, we investigate the electron transport properties across an all-carbon molecular junction consisting of C20 molecules suspended between two semi-infinite carbon nanotubes. It is shown that the conductances are quite sensitive to the number of C20 molecules between electrodes for both configuration CF1 and double-bonded models： the conductances of C20 dimers are markedly smaller than those of monomers. The physics is that incident electrons easily pass the C20 molecules and are predominantly scattered at the C20-C20 junctions. Moreover, we study the doping effect of such molecular junction by doping nitrogen atoms substitutionally. The bonding property of the molecular junction with configuration CF1 has been analysed by calculating the Mulliken atomic charges. Our results have revealed that the C atoms in N-doped junctions are more ionic than those in pure-carbon ones, leading to the fact that N-doped junctions have relatively large conductance.     

Au电极连接富勒烯C32分子的电子结构与传输特性

采用基于密度泛函理论(DFT)和非平衡格林函数(NEGF)的第一性原理方法对富勒烯C₃₂分子及在C₃₂分子的距离最远的两个碳原子处连接Au(1,1,1)电极的分子器件进行了电子结构和电子输运性质的研究.考虑到中间分子与Au电极间距离变化的情况,通过计算得出了在不同距离下分子器件的电子传输谱和I-V特性,分析了各器件的电子结构和电子输运特性产生的原因,并分析了电极与中间分子的连接距离及门电压对分子器件电子输运的影响.得出了电极与所连接的中间分子之     

Design and First-principles Study of a Fullerene Molecular Device

By using open-ended armchair （6, 6） single-wall carbon nanotubes as electrodes, we investigate the electron transport properties of an all-carbon molecular junction based on the C82 molecule. We find the most stable system among different isomers by performing structural optimization calculations of the Cs2 isomers and the C82 extended molecules. The calculated results show that the C82 -C2 （3） isomer and the C82 extended molecule with C82-C2 isomer are most stable. For the all-carbon hybrid system consisting of C82-C2 extended molecules, it is shown that the Landauer conductance can be tuned over several orders of magnitude both by changing the distance between two electrodes and by changing the orientation of the C82 molecule or rotating one of the tubes around the symmetry axis of the system at a fixed distance. Also, we find the most stable distance between two electrodes from the total energy curve. This fact could make this all-carbon molecular system a possible candidate for a nanoelectronic switch. Moreover, we interpret the conductance mechanism for such a molecular device.     

Nickel cluster functionalised carbon nanotube for CO molecule detection: a theoretical study

Using spin-polarised density functional theory calculation single-walled carbon nanotube (SWCNT) whose sidewall is functionalised with nickel cluster is studied for its possible application in CO molecule sensing. We have chosen (6,0) SWCNT functionalised with Ni₁₃ cluster as the model for nanotube-cluster system. Changes in the properties of nanotube-cluster system brought by the CO molecule are reported. The CO molecule binding is energetically more favourable to the nanotube-cluster system than the pristine nanotube. The electronic properties are investigated in terms of density of states and bandstructure calculations. Pristine carbon nanotubes are intrinsically non-magnetic but nanotubes functionalised with nickel cluster are observed to have a huge magnetic moment which reduced on adsorbing CO molecule. The change in magnetisation upon CO adsorption may be detected using a suitable magnetometer. This result suggests the possibility of using carbon nanotube-cluster system to detect CO molecules. Bader charge analysis shows that CO molecule withdraws electronic charge from the cluster atoms. Nature of chemical bonding is studied with crystal orbital Hamilton population (–COHP) analysis.     

Nanotube field and one-dimensional fluctuations of C<Subscript>60</Subscript> molecules in carbon nanotubes

C₆₀ molecules encapsulated in carbon nanotubes interact by van der Waals forces with the tube walls. The nanotube field leads to orientational confinement of the C₆₀ molecules which depends on the nanotube radius. In small tubes with radius R_T≤7 ? a fivefold symmetry axis of the molecule coincides with the tube axis, the center of mass of the molecule being located on the tube axis. The interaction between C₆₀ molecules encapsulated in the nanotube is then described by a O₂-rotor model on a one-dimensional (1-d) liquid chain with coupling between orientational and displacive degrees of freedom but no long-range order. This coupling leads to a temperature-dependent chain contraction. The structure factor of the 1-d liquid is derived. In tubes with larger radius the molecular centers of mass are displaced off the tube axis. The distinction of two groups of peapods with on- and off-axis molecules suggests an explanation of the apparent splitting of A_g modes of C₆₀ in nanotubes measured by resonant Raman scattering.     

封装椭圆形C70的手性纳米管的理论表征

应用第一性原理计算,研究了椭圆形的C₇₀分子在碳纳米管中的可能取向．采用(14,7)单壁纳米管为原型材料,发现纳米管和C₇₀分子的弱化学相互作用是决定分子取向的决定因素．通过模拟扫描隧道显微镜图像和计算光学性质,发现封装的椭圆体C₇₀分子的局域电子结构敏感地依赖于分子取向     

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     

碳链输运对基团吸附的敏感性分析

基于局域原子轨道的密度泛函理论和非平衡格林函数方法,研究了碳链输运特性对分别吸附7种常见官能团NO₂, CN, CHO, Br, C₆H₅, C₅H₄N和NH₂时的敏感性. 计算表明,电流对C₆H₅和CHO的吸附最为敏感,其次是对CN和C₅H₄N的吸附,在某些偏压下电流有大幅度的下降,其值 关键词： 碳链 输运特性 密度泛函理论 非平衡格林函数     

Orientation effect on the electronic transport properties of C24 fullerene molecule

The transport properties of the cage-like molecule depend on its orientation between the electrodes, but the investigation on the mechanism has not been found. Using first-principle density-functional theory (DFT) and non-equilibrium Green’s function (NEGF) formalism for quantum transport calculation, we study the electronic transport properties of C₂₄ fullerene molecule with different orientations in Au–C₂₄–Au two-probe system. The effects of k-point sampling on the Brillouin zone are explored. Our results show that the negative differential resistance of C₂₄ molecule is found in such a system and can be tuned by the molecule's orientation in the two-probe system. We also proposed a mechanism for it. The I–V characteristic under bias voltage is determined. The present findings could be helpful for the application of the C₂₄ molecule in the field of single molecular devices or nanometer electronics.     

A first-principles study on the adsorption behaviour of methanol and ethanol over C59B heterofullerene

In the present study, the adsorption behaviour of methanol (CH₃OH) and ethanol (C₂H₅OH) molecules over heterofullerene C₅₉B surface is studied by density functional theory calculations. This heterofullerene is obtained from C₆₀ by substituting a carbon atom with a boron atom and relaxing self-consistently the structure to the local minimum. The adsorption of CH₃OH and C₂H₅OH on the C₅₉B is exothermic and the relaxed geometries are stable. The CH₃OH and C₂H₅OH adsorption can also induce a change in the highest occupied molecular orbital and the lowest unoccupied molecular orbital energy gap of the nanocage. The dehydrogenation pathways of CH₃OH and C₂H₅OH via O–H and C–H bonds scission are also examined. The results indicate that O–H bond scission is the most favourable pathway on the C₅₉B surface.     

MgO-decorated carbon nanotubes for CO2 adsorption: first principles calculations

The global greenhouse effect makes it urgent to deal with the increasing greenhouse gases.In this paper the performance of MgO-decorated carbon nanotubes for CO 2 adsorption is investigated through first principles calculations.The results show that the MgO-decorated carbon nanotubes can adsorb CO 2 well and are relatively insensitive to O 2 and N 2 at the same time.The binding energy arrives at 1.18 eV for the single-MgO-decorated carbon nanotube adsorbing one CO 2 molecule,while the corresponding values for O 2 and N 2 are 0.55 eV and 0.06 eV,respectively.In addition,multi-molecule adsorption is also proved to be very satisfactory.These results indicate that MgO-decorated carbon nanotubes have great potential applications in industrial and environmental processes.     

紫外激光和压力共同作用下C60-peapod的聚合相变研究

采用气相扩散方法将C₆₀分子填充到单壁碳纳米管(SWNTs)中，制备出高填充比率的豆荚形纳米材料C₆₀@SWNT，又称为peapod.用金刚石对顶砧(DAC)装置获得高压，在高压下同时利用紫外激光处理样品，通过激光和压力的共同作用研究了C₆₀分子在碳管内的聚合相变.在21.5GPa高压下，同时紫外激光(325nm)照射30min后，拉曼光谱表明C₆₀分子在碳管内发生了聚合，形成一维链状O相聚合结构，且该相变是不可逆的. 关键词： 60 peapod')" href="#">C₆₀ peapod 紫外激光 高压 拉曼光谱     

Hydrogen storage in BC3 composite single-walled nanotube:a combined density functional theory and Monte Carlo investigation

This paper applies a density functional theory(DFT) and grand canonical Monte Carlo simulations(GCMC) to investigate the physisorptions of molecular hydrogen in single-walled BC 3 nanotubes and carbon nanotubes.The DFT calculations may provide useful information about the nature of hydrogen adsorption and physisorption energies in selected adsorption sites of these two nanotubes.Furthermore,the GCMC simulations can reproduce their storage capacity by calculating the weight percentage of the adsorbed molecular hydrogen under different conditions.The present results have shown that with both computational methods,the hydrogen storage capacity of BC 3 nanotubes is superior to that of carbon nanotubes.The reasons causing different behaviour of hydrogen storage in these two nanotubes are explained by using their contour plots of electron density and charge-density difference.     

Computational analysis of effect of modification on the interfacial characteristics of a carbon nanotube-polyethylene composite system

In this study, the non-covalent association of single-walled nanotube (SWNT) with polyethylene (PE) molecule and the influence of sidewall modification on the interfacial bonding between the SWNTs and polymer were investigated using molecular mechanics (MM) and molecular dynamics (MD) simulations. The model of interaction between the initially separated PE and SWNT fragments, which can be either wrapping or filling, was computed. The possible extension of polymers wrapping or filling SWNTs can be used to structurally bridge the SWNTs and polymers to significantly improve the load transfer between them when SWNTs are used to produce nanocomposites. The interfacial bonding characteristics between the single-walled nanotubes, on which -COOH, -CONH₂, -C₆H₁₁, or -C₆H₅ groups have been chemically attached, and the polymer matrix were also investigated by performing pullout simulations. The results show that appropriate functionalization of nanotubes at low densities of functionalized carbon atoms drastically increase their interfacial bonding and shear stress between the nanotubes and the polymer matrix, where chemisorption with -C₆H₅ groups to as little as 5.0% of the nanotube carbon atoms increases the shear stress by about 1700%. Furthermore, this suggests the possibility to use functionalized nanotubes to effectively reinforce other kinds of polymer-based materials as well.     

Optical properties of fullerene and non-fullerene peapods

Single-wall carbon nanotubes (SWNTs) encapsulating fullerenes, so-called fullerene peapods, were synthesized in high yield by using diameter-selected nanotubes as pods. Transmission electron microscopy revealed high-density fullerene chains inside the nanotubes. X-ray-diffraction measurements indicate 85% filling for C₆₀ and 72% filling for C₇₀ molecules as a total yield. Interestingly, C₆₀ peas do not show any thermal expansion while C₇₀ peas show normal behavior. Room-temperature Raman spectra show one-dimensional photopolymerization of C₆₀ inside nanotubes by blue-laser irradiation, suggesting molecular rotation inside them. In C₇₀ peapods, no photopolymerization was observed but the relative Raman intensity of each peak is different from the C₇₀ 3D crystal. This is probably caused by mixing of two different crystal structures in C₇₀ peas. Furthermore, we synthesized Zn-diphenylporphyrin peapods. Optical absorption and Raman spectra suggest that the encapsulated molecules are deformed by interaction with the SWNT. Received: 12 November 2001 / Accepted: 3 December 2001 / Published online: 4 March 2002     

Quasi-one-dimensional fullerene-nanotube composites: Structure, formation energetics, and electronic properties

Carbon nanotubes coated with close-packed C₆₀ (or C₇₀) fullerenes, which are “attached” to the nanotubes by van der Waals forces, are considered and classified as a new class of nanocomposites. Semiempirical and molecular-dynamics calculations reveal the most energetically stable systems and show that a topological (Stone-Wales) defect on a nanotube can promote a more favorable “attachment” of fullerene to the nanotube. It has been shown that the molecular interaction of the fullerene coating with the nanotube leads to a significant change in its electronic spectrum, namely, to the formation of minibands including a large number of branches associated with the lift of the degeneracy of levels of C₆₀ and to the consolidation of branches of the carbon nanotube into the Brillouin zone smaller than that in the carbon nanotube. This fact should strongly change the interaction of light with such a nanocomposite as compared to carbon nanotubes and fullerenes, which provides prospect of its application in photovoltaics.