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.     

[C2MIM]+在碳纳米管中结构和性质的理论研究

采用密度泛函理论方法,系统研究了1-乙基-3-甲基咪唑离子 ( [C2MIM]+ ) 在三种不同管径的碳纳米管中的稳定结构、相互作用能和分子轨道性质. 研究表明,随着碳纳米管管径的增加,[C2MIM]+在碳纳米管内的稳定结构从居中的位置越发靠近碳纳米管的管壁,其与碳纳米管的结合能也从-45.52 kcal/mol降低到-39.45 kcal/mol. 通过分析[C2MIM]+在不同尺寸碳纳米管中的分子轨道排布,发现研究体系的HOMO轨道和LUMO轨道主要是局域在碳纳米管上,电子跃迁表现为π→π*,表明[C2MIM]+与碳纳米管之间为弱的范德华作用. 本研究为理解离子液体与碳纳米管之间的相互作用提供了重要的理论基础.     

A hybrid continuum and molecular mechanics model for the axial buckling of chiral single-walled carbon nanotubes

The purpose of this study is to describe the axial buckling behavior of chiral single-walled carbon nanotubes (SWCNTs) using a combined continuum-atomistic approach. To this end, the nonlocal Flugge shell theory is implemented into which the nonlocal elasticity of Eringen incorporated. Molecular mechanics is used in conjunction with density functional theory (DFT) to precisely extract the effective in-plane and bending stiffnesses and Poisson's ratio used in the developed nonlocal Flugge shell model. The Rayleigh-Ritz procedure is employed to analytically solve the problem in the context of calculus of variation. The results generated from the present hybrid model are compared with those from molecular dynamics simulations as a benchmark of good accuracy and excellent agreement is achieved. The influences of small scale factor, commonly used boundary conditions and chirality on the critical buckling load are fully explored. It is indicated that the importance of the small length scale is affected by the type of boundary conditions considered.     

有限长扶手椅形单壁碳纳米管分子静电势的理论研究

在混合密度泛函B3LYP理论下,用3-21G基函数对有限长扶手椅形单壁碳纳米管(4,4)、(5,5)和(6,6)的构型进行优化和分子静电势计算.结果表明:除近核区域为正常的正电势外,碳纳米管结构模型的管内和管外为负电势区域;在碳纳米管结构模型的管内,管心处均出现负电势的最小值,且负电势的绝对值随着碳纳米管的曲率降低而增大,管心轴线上静电势的变化随碳纳米管的曲率降低而减少,带电粒子流比较容易通过纳米管.     

Electronic structure, energetics and geometric structure of carbon nanotubes: A density-functional study

Based on the local density approximation (LDA) in the framework of the density-functional theory, we study the details of electronic structure, energetics and geometric structure of the chiral carbon nanotubes. For the electronic structure, we study all the chiral nanotubes with the diameters between 0.8 and 2.0 nm (154 nanotubes). This LDA result should give the important database to be compared with the experimental studies in the future. We plot the peak-to-peak energy separations of the density of states (DOS) as a function of the nanotube diameter (D). For the semiconducting nanotubes, we find the peak-to-peak separations can be classified into two types according to the chirality. This chirality dependence of the LDA result is opposite to that of the simple π tight-binding result. We also perform the geometry optimization of chiral carbon nanotubes with different chiral-angle series. From the total energy as a function of D, it is found that chiral nanotubes are less stable than zigzag nanotubes. We also find that the distribution of bond lengths depends on the chirality.     

Optimisation of stability and charge transferability of ferrocene-encapsulated carbon nanotubes

Ferrocene-encapsulated carbon nanotubes (Fc@CNTs) became promising nanocomposite materials for a wide range of applications due to their superior catalytic, mechanical and electronic properties. To open up new windows of applications, the highly stable and charge transferable encapsulation complexes are required. In this work, we designed the new encapsulation complexes formed from ferrocene derivatives (FcR, where R = –CHO, –CH₂OH, –CON₃ and -PCl₂) and single-walled carbon nanotubes (SWCNTs). The influence of diameter and chirality of the nanotubes on the stability, charge transferability and electronic properties of such complexes has been investigated using density functional theory. The calculations suggest that the encapsulation stability and charge transferability of the encapsulation complexes depend on the size and chirality of the nanotubes. FcR@SWCNTs are more stable than Fc@SWCNTs at the optimum tube diameter. The greatest charge transfer was observed for FcCH₂OH@SWCNTs and Fc@SWCNTs since the Fe d levels of FcCH₂OH and Fc are nearly equal and close to the Fermi energy level of the nanotubes. The obtained results pave the way to the design of new encapsulated ferrocene derivatives which can give rise to higher stability and charge transferability of the encapsulation complexes.     

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.     

Structural and electronic properties of endohedral doped SWCNTs: A DFT study

The structural and electronic properties of semiconductors (Si and Ge) and metal (Au and Tl) atoms doped armchair (n, n) and zigzag (n, 0); n=4–6, single wall carbon nanotubes (SWCNTs) have been studied using an ab-initio method. We have considered a linear chain of dopant atoms inside CNTs of different diameters but of same length. We have studied variation of B.E./atom, ionization potential, electron affinity and HOMO–LUMO gap of doped armchair and zigzag CNTs with diameter and dopant type. For armchair undoped CNTs, the B.E./atom increases with the increase in diameter of the tubes. For Si, Ge and Tl doped CNTs, B.E./atom is maximum for (6, 6) CNT whereas for Au doped CNTs, it is maximum for (5, 5) CNTs. For pure CNTs, IP decreases slightly with increasing diameter whereas EA increases with diameter. The study of HOMO–LUMO gap shows that on doping metallic character of the armchair CNTs increases whereas for zigzag CNTs semiconducting character increases. In case of zigzag tubes only Si doped (5, 0), (6, 0) and Ge doped (6, 0) CNTs are stable. The IP and EA for doped zigzag CNTs remain almost independent of tube diameter and dopant type whereas for doped armchair CNTs, maximum IP and EA are observed for (5, 5) tube for all dopants.     

A computational study of silicon-doped aluminum phosphide nanotubes

We performed density functional theory (DFT) calculations to investigate the properties of silicon-doped (Si-doped) models of representative (4,4) armchair and (6,0) zigzag aluminum phosphide nanotubes (AlPNTs). The structures were allowed to relax and the chemical shielding (CS) parameters were calculated for the atoms of optimized structures. The results indicated that the band gap energies and dipole moments detect the effects of dopant. The CS parameters also indicated that the Al and P atoms close to the Si-doped region are such reactive atoms, which make the Si-doped AlPNTs more reactive than the pristine AlPNTs. Moreover, replacement of P atom by the Si atom makes AlPNT more reactive than the replacement of Al atom by the Si atom.     

First principle study of unzipped zinc oxide nanotubes

First principle calculations have been employed in order to explain the dangling bonds behavior in the rolling up of a zinc oxide nanoribbon (ZnONR) to construct a single-walled zinc oxide nanotube (SWZnONT). Our results show in armchair ZnONR two degenerative dangling bonds split and moved up to higher energies due to symmetry breaking of the system. By more rolling up (increasing the curvature), the energy gap is increased by increasing of curvature.     

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.     

Beryllium oxide (BeO) nanotube provides excellent surface towards adenine adsorption: A dispersion-corrected DFT study in gas and water phases

Zigzag (5, 0) BeO nanotube (BeONT) has been examined in detail towards adsorption properties of adenine nucleobase on its surface via D2-DFT calculation method in the gas and water phases. A detailed surface study reveals that there are four orientations for nucleobase adsorption that none of the vibrational spectrums demonstrated imaginary frequency, recognizing that all of the relaxed structures are at the minimum of energy. The minimum and maximum adsorption energies are both in chemisorption regime with calculated values of −140 (−118 BSSE corrected) and −191 (−168 BSSE corrected) in the gas phase, and −181 and −310 kJ/mol in the water phase, using meta-hybrid functional (ꞷB97XD) and 6-31G** basis set. For all positions, BeONT showed p-type semiconducting property because of receiving electronic charge from adenine molecule. Our findings suggest that BeONT could be used as a possible strong carrier for adenine molecule in practical applications.     

Interaction of alkanethiols with single-walled carbon nanotubes: First-principles calculations

We report the results of our first-principles study based on density functional theory on the interaction of alkanethiols with both defected and defect-free single-walled carbon nanotube (SWCNT). The adsorption energies are calculated for various configurations such as alkanethiol molecule approaching to defect sites heptagon, hexagon, and pentagon in defective tube, and another case where the alkanethiol approaching to hexagon in defect-free nanotube. The calculated results showed that alkanethiols are rather strongly bound to the outer surface of both the defected and defect-free carbon nanotubes with the binding energy of about −50.58 kcal/mol, consistent with the experimental result. We also find that alkanethiols prefer to be adsorbed on the hexagon ring site of defect-free nanotube. Furthermore, the effect of alkanethiols chain length on the adsorption of alkanethiols on carbon nanotubes has been investigated, and the obtained results reveal that the longer alkanethiols bind rather more strongly to the nanotube surface.     

Effects of various defects on the electronic properties of single-walled carbon nanotubes: A first principle study

The geometries,formationenergies and electronic band structures of （8, 0） and （14, 0） singlewailed carbon nanotubes （SWCNTs） with various defects, inehlding vaeaney, Stone-Wales defect, and octagon pentagon pair defect, have been investigated within the framework of the density- huictional theory （DFT）, and the influence of the concentration within the same style of deflect on the physical and chenfical properties of SWCNTs is also studied. The results suggest that the existeilcc of vacancy and octagon-pentagon pair deflect both reduce the band gap, whereas the SW- defect induces a band gap opening in CNTs. More int, erestingly, the band gaps of （8, 0） and （14, 0） SWCNTs eonfigurations with two octagon pentagon pair defect presents 0.517 eV and 0.163/eV, which arc a little smaller than the perfectt CNTs. Furthermore, with the concentration of defects increasing, there is a decreasing of band ga.p making the two types of SWCNTs change from a semiconductor to a metallic conductor.     

A density-functional-theory-based finite element model to study the mechanical properties of zigzag phosphorene nanotubes

In this paper, the density functional theory calculations are used to obtain the elastic properties of zigzag phosphorene nanotubes. Besides, based on the similarity between phosphorene nanotubes and a space-frame structure, a three-dimensional finite element model is proposed in which the atomic bonds are simulated by beam elements. The results of density functional theory are employed to compute the properties of the beam elements. Finally, using the proposed finite element model, the elastic modulus of the zigzag phosphorene nanotubes is computed. It is shown that phosphorene nanotubes with larger radii have larger Young's modulus. Comparing the results of finite element model with those of density functional theory, it is concluded that the proposed model can predict the elastic modulus of phosphorene nanotubes with a good accuracy.     

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.     

Nanoelectromechanical devices with carbon nanotubes

Thanks to their excellent mechanical properties as well as interesting electrical characteristics, carbon nanotubes are among the most widely used materials for the study of electromechanical properties. This review paper presents the physical properties and the potential applications of carbon nanotube based nanoelectromechanical devices. We present an overview of fabrication methods followed by a discussion of the physical properties of CNT-NEMS. Finally some potential applications are discussed.     

Boron nitride nanotubes with quadrangular cross sections: Density functional studies

Density functional theory (DFT) calculations have been performed to investigate the availabilities and properties of boron nitride nanotubes (BNNTs) with quadrangular cross sections. To achieve the purposes, the original structure of a representative BNNT was individually decorated by the carbon and silicon atoms to make the C-BNNT and Si-BNNT models. The sp³ hybridizations were set for the C and Si atoms to make possible the formation of the quadrangular cross sections for the BNNTs. The optimized results indicated that the investigated models could be stabilized; however, they showed different properties. The atomic scale properties based on computations of quadrupole coupling constants (C_Q) also approved different properties for the C-BNNT and Si-BNNT models. Moreover, the C_Q parameters indicated that the properties of C-BNNT could be considered similar to the original BNNT; however, more discrepancies were observed for the Si-BNNT.     

Chemical shielding properties for BN,BP, AlN,and AlP nanocones: DFT studies

The properties of boron nitride (BN), boron phosphide (BP), aluminum nitride (AlN), and aluminum phosphide (AlP) nanocones were investigated by density functional theory (DFT) calculations. The investigated structures were optimized and chemical shielding (CS) properties including isotropic and anisotropic CS parameters were calculated for the atoms of the optimized structures. The magnitudes of CS parameters were observed to be mainly dependent on the bond lengths of considered atoms. The results indicated that the atoms could be divided into atomic layers due to the similarities of their CS properties for the atoms of each layer. The trend means that the atoms of each layer detect almost similar electronic environments. Moreover, the atoms at the apex and mouth of nanocones exhibit different properties with respect to the other atomic layers.