Magnetic properties and electronic structures of hcp Fe,Co and Ni nanowires encapsulated in a zigzag (12,0) BN nanotube

The magnetic properties and electronic structures of ferromagnetic nanowires (FM=Fe, Co and Ni) encapsulated inside a zigzag (12,0) boron nitride nanotube (BNNT) are investigated by first-principle calculations. The relaxed geometry structures of FM/BNNT systems have only slightly changed. Formation energy analysis shows that the combining processes of Co/BNNT and Ni/BNNT systems are exothermic, and therefore the Co and Ni nanowires can be encapsulated into a semiconducting zigzag (12,0) BNNT and form stable hybrid structures. The charges are transferred from ferromagnetic nanowires to more electronegative BNNTs, and the formed FM–N bonds have covalent bond characteristics. The magnetic moments of FM/BNNT systems are smaller than those of the freestanding ferromagnetic nanowires, especially for the atoms on the outermost shell of the nanowires. The stable FM/BNNT systems exhibit higher magnetic moments, which can be useful for a wide variety of next-generation nanoelectronic device components.     

Electromechanical buckling analysis of boron nitride nanotube using molecular dynamic simulation

In this paper, the effect of electric field on axial buckling of boron nitride nanotubes is investigated. For this purpose, molecular dynamics simulation and continuum mechanics are used for the first time simultaneously. In molecular dynamics simulation, the potential between boron nitride atoms is considered as Tersoff and Timoshenko beam theory is used in continuum mechanics. In this paper, buckling of zigzag and armchair boron nitride nanotubes are investigated. Here, the effects of the electric field and the length of the boron nitride nanotube on the critical load are investigated and it is shown that the effect of the electric field is different with respect to the arrangement of atoms in the boron nitride nanotubes. In fact, the electric field creates axial and torsional loads on the zigzag and armchair nanotube, respectively. Axial buckling of the zigzag nanotube is dependent on the electric field, whereas in the armchair nanotubes, the electric field changes have no effect on the axial buckling. To better understand the impact of the electric field on axial buckling, these results are compared with the continuum mechanics.     

弯曲BN纳米片的电子性质及其调制

BN纳米片是具有一定宽度、无限长度的一维蜂窝构型单层带状氮化硼材料,弯曲的BN纳米片因为P z轨道旋转,将表现出一定的独特的电子性质.通过第一性原理计算,利用MS(Material Studio)中的DMOL3(local density functional calculations on molecules)软件计算了Zigzag和Armchair型BN纳米片弯曲以后的能带结构.BN纳米带的带隙会随着弯曲角度的变化而改变,以Armchair型BN纳米带的变化较为明显;在弯曲的基础上再加入外电场,却是Zigzag型BN纳米带的带隙变化更显著.当电场加大到一定的值,纳米带就会从半导体变为金属,并且这一临界电场值的大小和纳米带的弯曲程度有关.电场对带隙的调制还和纳米带的尺寸有关系,电场对大尺度的纳米带的调控性更好,从半导体转变为金属所需要的电场值要更小.     

Tuning the electronic and magnetic properties of boron nitride nanotubes

Density Functional Theory is used to investigate the effect of altering the B/N ratio and carbon doping on the electronic and magnetic structure of zigzag, (7, 0) and armchair (5, 5) boron nitride nanotubes. The calculations indicate that increasing the boron content relative to the nitrogen content significantly reduces the band gap to a value typical of a semiconductor. Calculations of carbon doped semiconducting BN tubes, which have more boron atoms than nitrogen atoms have a net spin and a difference in the density of states at the valence band between the spin up and spin down state.     

Structural and electronic properties of BN M?bius stripes

In the present contribution it is applied first-principles calculations to investigate the electronic structure of boron nitride M?bius stripes, with armchair and zigzag configurations, obtained from boron nitride nanoribbons using a ??cut?? and ??glue?? process. The results show that the structural stability strongly depends on the length and width of the stripe. It is also found that the energy gap and work function depends on the structure chirality. Due to the formation of an antiphase boundary, zigzag stripes present tunable electronic properties, with significant potential for technological applications.     

Structural,electronic and magnetic properties of Fe(1−x)Cox alloy nanowires encapsulated inside (10,0) boron nitride nanotube

The structural, electronic and magnetic properties of Fe–Co alloy nanowires encapsulated inside zigzag (10,0) boron nitride nanotube (BNNT) are investigated by ab initio calculations. Similar to pristine nanotube, the opposite directional relaxations for the N atoms (move outwards) and B atoms (move inwards) from their initial positions are observed for outside BNNT although with the Fe–Co alloy nanowires inside, but the outward relaxations of the N atoms bonding to the Fe or Co atoms are smaller due to their attractions. The combining processes of Fe–Co/BNNT composites are endothermic when Co concentration x≤0.6 and exothermic x>0.6, and the most stable Fe–Co/BNNT composite is at Co concentration x=0.8. So the semiconducting (10,0) BNNT can be used to shield the Co-rich Fe–Co nanowires. The charges are transferred from Fe–Co nanowires to BNNT and the formed Co–N bonds have covalent bond as well as slight ionic bond characters. Although (10,0) BNNT is nonmagnetic and a decrease in the magnetic moment is found after Fe–Co nanowires are encapsulated inside (10,0) BNNT, the Fe–Co/BNNT composites still have large magnetic moment, reflecting they can be utilized in magnetic storage and ultra high-density magnetic recording devices.     

First-principles calculations of BC4N nanostructures: stability and electronic structure

In this work, we apply first-principles methods to investigate the stability and electronic structure of BC₄N nanostructures which were constructed from hexagonal graphite layers where substitutional nitrogen and boron atoms are placed at specific sites. These layers were rolled up to form zigzag and armchair nanotubes, with diameters varying from 7 to 12 Å, or cut and bent to form nanocones, with 60^° and 120^° disclination angles. The calculation results indicate that the most stable structures are the ones which maximize the number of B–N and C–C bonds. It is found that the zigzag nanotubes are more stable than the armchair ones, where the strain energy decreases with increasing tube diameter D, following a 1/D ² law. The results show that the 60^° disclination nanocones are the most stable ones. Additionally, the calculated electronic properties indicate a semiconducting behavior for all calculated structures, which is intermediate to the typical behaviors found for hexagonal boron nitride and graphene.     

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.     

Tuning the electronic and magnetic properties of the Si nanoribbons through dangling bond

Combined with three spin configurations, the effects of the dangling bonds on the electronic and magnetic properties of both zigzag edge and armchair edge Si nanoribbions (ZSiNR and ASiNR) have been investigated systematically by the first-principles calculations in the local spin-density function theory. The dangling bonds at one edge or both edges make ZSiNR to transform from ferromagnetic state of the perfect ZSiNR to antiferromagnetic state. However, the dangling bonds at one edge and both edges make ASiNR to transform from nonmagnetic semiconductor of the perfect ASiNR to ferromagnetic and antiferromagnetic metals, respectively. Furthermore, the magnetic moment of the ferromagnetic state increases for the perfect bare one edge and bare both edges successively for either ZSiNR or ASiNR.     

Strain Effects on Electronic Properties of Boron Nitride Nanoribbons

We investigate the strain effects on the electronic properties of boron nitride nanoribbons （BNNFts） by using firstprinciples calculations. The results show that the energy gap of BNNRs with both armchair edges （A-BNNRs） and zigzag edges （Z-BNNFts） decreases as the strain increases. As strain increases, the energy gaps of Z-BNNRs decrease rapidly as the width increases and reduce significantly to small values, which makes Z-BNNRs change from wide-gap to narrow-gap semiconductors.     

轴压和扭转复合载荷作用下氮化硼纳米管屈曲行为的分子动力学模拟

采用分子动力学方法模拟了氮化硼纳米管在轴压和扭转复合荷载作用下的屈曲和后屈曲行为.在各加载比例下,给出了初始线性变形阶段和后屈曲阶段原子间相互作用力的变化,确定了屈曲临界荷载关系.通过对屈曲模态的细致研究,从微观变形机理上分析了纳米管对不同外荷载力学响应的差异.研究结果表明,扶手型和锯齿型纳米管均呈现出非线性的屈曲临界荷载关系,复合加载下的屈曲行为具有强烈的尺寸依赖性.温度升高将导致屈曲临界荷载的下降,且温度的影响随加载比例的变化而变化.无论在简单加载或复合加载中,同尺寸的碳纳米管均比氮化硼纳米管具有更强地抵抗屈曲荷载的能力.     

Strain effect on transport properties of hexagonal boronben nitride nanoribbons

The transport properties of hexagonal boron--nitride nanoribbons under the uniaxial strain are investigated by the Green's function method. We find that the transport properties of armchair boron--nitride nanoribbon strongly depend on the strain. In particular, the features of the conductance steps such as position and width are significantly changed by strain. As a strong tensile strain is exerted on the nanoribbon, the highest conductance step disappears and subsequently a dip emerges instead. The energy band structure and the local current density of armchair boron--nitride nanoribbon under strain are calculated and analysed in detail to explain these characteristics. In addition, the effect of strain on the conductance of zigzag boron--nitride nanoribbon is weaker than that of armchair boron nitride nanoribbon.     

The X (X = C, Si and Ge) doped BN nanotube: A computational study

We have performed density functional theory (DFT) calculations to investigate the influence of X-doping (X = C, Si and Ge) on the properties of the electronic structure of the zigzag boron-nitride nanotubes (BNNTs). A single boron and nitrogen atom in the representative (10, 0) BNNT are doped by the X atoms. Electric field gradient (EFG) tensors have been calculated for the different models of the investigated BNNT and converted to quadrupole coupling constants (CQ) for B-11 and N-14 atoms. Our results indicated that the CQ parameters are changed for N-X bonds more than those for B-X ones. The calculations were carried out using the Gaussian 03 software package.     

A first-principles investigation on the effect of the divacancy defect on the band structures of boron nitride (BN) nanoribbons

On the basis of the comprehensive first-principles computations, we investigated the geometries, electronic and magnetic properties of zigzag and armchair boron nitride nanoribbons (BNNRs) with the divacancy defect of 5–8–5 ring fusions formed by removing B–N pair, where the defect orientation and position are considered. Our computed results reveal that all of the defective BNNRs systems can uniformly exhibit nonmagnetic semiconducting behavior, and the formation of the divacancy 5–8–5 defect can significantly impact the band structures of BNNRs with not only the zigzag but also armchair edges, where their wide band gaps are reduced and the defect orientation and position play an important role. Clearly, introducing divacancy defect can be a promising and effective approach to engineer the band structures of BNNRs, and the present computed results can provide some valuable insights for promoting the practical applications of excellent BN-based nanomaterials in the nanodevices.     

Density functional study of zigzag BN nanotubes with equivalent ends

A density functional theory (DFT) study was performed on representative model of zigzag boron nitride nanotubes (BNNTs) with equivalent ends. Two models of (6,0) BNNTs were considered in the calculations in which a belt composed of carbon atoms was substituted instead of boron and nitrogen atoms in the middle of the nanotube. Hence, model 1 was created with two equivalent B-ends and model 2 was created with two equivalent N-ends. The optimization process and also the calculated electric field gradient (EFG) tensors in two models of BNNT remarkably revealed that the electronic structure properties of those nuclei located at the end of nanotube are duplicated in the considered models of BNNTs. The calculations were performed at the level BLYP method and 6-31G* standard basis set using GAUSSIAN 98 package of program.     

5d过渡金属原子掺杂氮化硼纳米管的第一性原理计算

采用基于密度泛函理论的第一性原理计算方法,研究了当氮化硼纳米管（BNNT）中的B原子和N原子被5d过渡金属原子（Lu,Hf,Ta,W,Re,Os,Ir,Pt,Au,Hg）取代时BNNT的几何结构、电子结构和磁性性质. 作为对比,给出了理想BNNT,B缺陷体系（V_B）和N缺陷体系（V_N）的相应结果. 研究发现：5d原子取代B（B_5d）时体系的局域对称性接近于C_3v,但是取代N（N_5d）时体系的局域对称性偏离C_3v对称性较大;利用相同的5d原子进行掺杂时,B_5d的成键能比N_5d的成键能大;对于B_5d或者N_5d,其成键能基本上随着5d原子的原子序数的增大而降低;掺杂体系中出现了明显的杂质能级,给出了态密度等结果;不同掺杂情况的磁矩不同,取代B 时体系的总磁矩呈现出较强的规律性. 利用对称性和分子轨道理论解释了5d原子取代B时杂质能级的产生和磁性的变化规律. 关键词： 第一性原理计算 5d过渡金属原子 氮化硼纳米管 密度泛函理论     

Mechanism of local stress release in armchair single-wall zinc oxide nanotube under tensile loading

The deformation mechanism of zinc oxide (ZnO) nanotube has been first examined by molecular dynamics. The result demonstrated that ZnO nanotubes relax it excess strain via the phase transformation from an armchair structure to a fourfold-coordinated structure, then to a zigzag structure, which is started by a slip deformation. In contrast to carbon, silicon carbide, and boron nitride nanotubes, they relax it local stress via the transformation of the Stone?CWales transformation. After yielding, the 8-4 dislocation loops are found and the numbers of 8-4 dislocation loops grow up, which relax the tensile strain at the necking region and leads the work hardening. Finally, the nanotube is broken down by crack deformation at the interface between different phases.     

Effect of doping on electronic properties of double-walled carbon and boron nitride hetero-nanotubes

The effect of boron nitride (BN) doping on electronic properties of armchair double-walled carbon and hetero-nanotubes is studied using ab initio molecular dynamics method. The armchair double-walled hetero-nanotubes are predicted to be semiconductor and their electronic structures depend strongly on the electronic properties of the single-walled carbon nanotube. It is found that electronic structures of BN-doped double-walled hetero-nanotubes are intermediate between those of double-walled boron nitride nanotubes and double-walled carbon and boron nitride hetero-nanotubes. Increasing the amount of doping leads to a stronger intertube interaction and also increases the energy gap.     

六角氮化硼纳米带的几何和电子结构理论研究

本文采用密度泛函B3LYP方法在6-31G*水平上,对一系列不同宽度的锯齿型和扶手椅型六角氮化硼纳米带进行了理论研究。结果表明纳米带宽度对体系的性质有规律性的影响。随着宽度的增加,纳米带不同位置的硼氮键键长差异逐步减小从而提高了整个体系的共轭性;锯齿型纳米带的能隙单调减小而扶手椅型纳米带的能隙在减小的同时出现振荡,且振幅随宽度逐渐减小。锯齿型氮化硼纳米带的化学势在特定宽度出现了极值点。前线分子轨道的分布随着宽度的增加出现了非均匀分布,呈现出向边界偏移的现象。     

六角氮化硼纳米带的几何和电子结构理论研究

本文采用密度泛函B3LYP方法在6-31G*水平上，对一系列不同宽度的锯齿型和扶手椅型六角氮化硼纳米带进行了理论研究。结果表明纳米带宽度对体系的性质有规律性的影响。随着宽度的增加，纳米带不同位置的硼氮键键长差异逐步减小从而提高了整个体系的共轭性；锯齿型纳米带的能隙单调减小而扶手椅型纳米带的能隙在减小的同时出现振荡，且振幅随宽度逐渐减小。锯齿型氮化硼纳米带的化学势在特定宽度出现了极值点。前线分子轨道的分布随着宽度的增加出现了非均匀分布，呈现出向边界偏移的现象。