扶手椅型碳化硅纳米管电子结构和光学性质的研究

本文基于密度泛函理论研究了扶手椅型碳化硅纳米管(SiCNT)的电子结构、成键机制以及其光学性质。研究结果表明:当碳和硅的原子比为1∶1时,SiCNT的结构最为稳定,并且表现出诸多的优良性质。通过分析计算结果我们发现,SiCNT是间接带隙材料,并且管子的带隙随着直径的增加而增加。从SiCNT的轨道图谱中我们看到碳和硅原子之间属于sp2杂化,同时硅原子周围的电子密度明显要低于碳原子周围的电子密度。对能态密度的计算我们得知碳原子和硅原子分别主导价带和导带。与其它纳米管(BN)有所不同,SiCNT的光学性质更接近于各向同性材料。     

锯齿型与扶手椅型碳化硅纳米管光电性质第一性原理研究

本文基于密度泛函理论计算分析了手性参数为(17,0)、(20,0)、(26,0) (10,10)、(12,12)、(15,15)的碳化硅纳米管的能带图,态密度及主要光学性质。结果表明：锯齿型与扶手椅型碳化硅纳米管均具有明显的半导体性质;在相近直径下,扶手椅型碳化硅纳米管带隙宽度要大于锯齿型碳化硅纳米管的带隙宽度;碳化硅纳米管的光吸收峰在100nm~200nm之间,可用于制作紫外线探测器件。     

氧化镁纳米管团簇电子结构的密度泛函研究

用密度泛函理论（DFT）的杂化密度泛函B3LYP方法在6-31G（d）基组水平上对MgO纳米管团簇的二元环双管、三元环、三元环双管三种构型共21个团簇进行优化,对各构型的平均结合能、能隙、平均原子电荷以及总电荷密度进行了理论研究. 结果表明,平均结合能和配位数呈线性关系;随着纳米管的生长,团簇的稳定性增加,其中以三元环纳米管最为稳定;生长过程中发生原子间的电荷转移现象,预测出至无限长时的平均原子电荷分别为1298,1270,1306;混合离子共价键始终存在于MgO纳米管团簇之中. 关键词： 氧化镁 纳米管团簇 密度泛函理论 电子结构     

金基纳米管AunSi12 (n=25-60)的奇异结构与电磁特性预测

应用相对论效应的密度泛函理论,系统研究了一系列稳定的中空类管状Au_nSi₁₂(n=25, 30, 35, 40, 45, 50, 55, 60)团簇. Au_nSi₁₂可以通过在不同长度的单壁Au纳米管(5, 5)的两端戴帽由二十面体Au₂₀Si₁₂平分的两个相同半球构建而成.计算结果显示,Si原子的掺杂使得Au_nSi₁₂的结构变得更加紧密且加强了相应的类管状Au团簇的稳定性.最高占据分子轨道(HOMO)和最低未占据分子轨道(LUMO)之间的能隙值在0.041 eV至0.138 eV区间,表明Au_nSi₁₂具有较高的化学活性.电子结构分析显示,Si原子和Au原子之间的p-d轨道杂化在形成和维持Au_nSi₁₂的类管状结构方面发挥了重要作用.Hirshfeld电荷分析显示,电荷从Au原子转移到Si原子上,Au_n...     

高压对氮化硼纳米管的几何结构、电子结构和光学性质的影响

运用密度泛函理论平面波赝势方法(PWP)和广义梯度近似(GGA),计算研究了纳米管BN(5,5)在不同压力条件下的几何结构、电子结构和光学性质. 在高压条件下管口形状发生了较大的变化. 与闪锌矿结构BN比较分析发现两种结构间存在一些性质上的差异：首先,在外压力作用下,BN(5,5)纳米管的带隙随压力增大而减小,变化率为-0.01795eV/GPa,而闪锌矿结构BN随压力增大而增大;其次光吸收谱在压力条件下,没有和闪锌矿结构BN一样发生“蓝移”,相反在红外方向有所拓展;但纳米管BN(5,5)电子的转移方向和 关键词： 氮化硼纳米管 密度泛函理论(DFT) 电子结构     

扶手椅型氮化镓纳米管电子结构与传输特性的研究（英文）

本文采用密度泛函理论和非平衡格林函数对扶手椅型氮化镓纳米管(n,n)(2≤n≤10)的电子结构和输运性质进行了研究.结果表明,所有的扶手椅型氮化镓纳米管都是间接带隙半导体,带隙随着纳米管直径的增加而增加,并且得到了两极体系下氮化镓纳米管的电流-电压曲线.氮化镓纳米管的半导体特性随着纳米管直径的增加越来越明显,电子态密度和电子透射光谱都具有脉冲型尖峰并且最大峰值随着n的增加而增加.这说明电子态密度和电子透射光谱峰在能量范围内,有较好的对应关系.     

SiC多型体几何结构与电子结构研究

采用平面波超软赝势法和范数不变赝势法对几种SiC多型体的几何结构、能带结构等进行了系统的研究.结果表明:6HSiC导带最低点在ML线上U点,用平面波超软赝势法计算时U点在(0000,0500,0176)点附近;而用范数不变赝势法计算时在导带最低点附近能带呈现不连续点,不连续点出现在(0000,0500,0178)点附近.两种赝势法计算结果相比,用平面波超软赝势法得到的导带最低点位置更靠近布里渊区M(0,05,0)点.在平面波超软赝势下,随着六角度的增加,cp,cpa增大的趋势较为明显,能隙和价带宽度变宽的趋势也较为明显.在计算极限内,绝对零度下4HSiC系统能量最低、最稳定,而Ewald能量显示3CSiC最稳定. 关键词： 密度泛函理论 电子结构 SiC     

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     

BN管状团簇到单壁纳米管的几何结构和电子性质

利用密度泛函理论(DFT),对氮化硼(BN)管状团簇的几何结构、稳定性和电子性质进行了研究.选取合适的BN结构单元作为结构生长基元,采用逐层生长的方式计算得到有限长度、不同截面尺寸的稳定管状团簇.结构中B-N交替排列,结构组成中的四元环和六元环数目均符合一般表达式.计算结果表明,通过适当组装管状团簇以及碳原子掺杂,可以制备出带隙可调的单壁氮化硼纳米管.     

硫化锌纳米管稳定性、电子性质和磁性质的比较研究

用第一性原理方法系统地研究硫化锌纳米管的稳定性、电子性质和掺杂磁性质.比较三种纳米管的稳定性.研究表明,六边形截面的双壁管的稳定性最高,相同截面的单壁管稳定性次之,而圆截面的之字形和扶手椅纳米管稳定性最低.电子能带结构计算表明它们都是直接带隙半导体.纳米管表面氢吸附后,六边形截面的单壁管转变为间接带隙半导体.研究了磁性原子掺杂六边形截面管的磁性质.发现掺杂纳米管的形成能比纯纳米管的形成能低,说明掺杂过程是一个放热反应.纳米管的总磁矩等于掺杂的磁性原子的磁矩.这些单掺杂纳米管在可调磁的新材料方面有潜在的应用价值.     

Effects of oxygen-containing defect complex on the electronic structures and transport properties of single-walled carbon nanotubes

The electronic structures and transport properties of (10,0)$(10,0)$ single-walled carbon nanotube ((10,0)$(10,0)$ (SWNT)) with oxygen-containing defect complex are investigated using density functional theory in combination with nonequilibrium Green?s function method. The complex delocalizes the local states of (10,0)$(10,0)$ SWNT induced by mono- and di-vacancy but strengthens the localization of the states induced by the Stone–Wales defect. As a result, the complex partially restores the transport properties of (10,0)$(10,0)$ SWNT with vacancies, but reduces the transmission of (10,0)$(10,0)$ SWNT with Stone–Wales defect. However, the oxygen-containing defect complex only slightly influences the transmission gap and threshold voltage of the system.     

A comparison study on the electronic structures,lattice dynamics and thermoelectric properties of bulk silicon and silicon nanotubes

In order to investigate the mechanism of the electron and phonon transport in a silicon nanotube(SiNT),the electronic structures,the lattice dynamics,and the thermoelectric properties of bulk silicon(bulk Si)and a SiNT have been calculated in this work using density functional theory and Boltzmann transport theory.Our results suggest that the thermal conductivity of a SiNT is reduced by a factor of 1,while its electrical conductivity is improved significantly,although the Seebeck coefficient is increased slightly as compared to those of the bulk Si.As a consequence,the figure of merit(ZT)of a SiNT at 1200 K is enhanced by 12 times from 0.08 for bulk Si to 1.10.The large enhancement in electrical conductivity originates from the largely increased density of states at the Fermi energy level and the obviously narrowed band gap.The significant reduction in thermal conductivity is ascribed to the remarkably suppressed phonon thermal conductivity caused by a weakened covalent bonding,a decreased phonon density of states,a reduced phonon vibration frequency,as well as a shortened mean free path of phonons.The other factors influencing the thermoelectric properties have also been studied from the perspective of electronic structures and lattice dynamics.     

Electronic structures and transport properties of sulfurized carbon nanotubes

The electronic and transport properties of side-walled sulfurized (8, 0) zigzag carbon nanotube were investigated by using density functional theory coupled with a non-equilibrium Green function approach. It is found that the adsorption of the sulfur chains largely reduces the bandgap of the semiconducting (8, 0) carbon nanotube, even changing it into a metallic one. More importantly, the transmission eigenstates around the Fermi level are contributed by not only the sulfur chains but also the complex system made of the sulfur chains and the single-walled carbon nanotube. Our results provide a method to improve the conductivity and utilization rate of the surface in the electrodes of supercapacitor which are made of the carbon nanotubes.     

单壁碳纳米管电子输运特性的稳定性分析

基于变形单壁碳纳米管能量色散关系,计算了碳纳米管最低导带的电子速度及有效质量随形变系数变化的各种曲线,以此推测碳纳米管输运性质的稳定性问题.计算结果表明：对于特定类型的碳纳米管,只当其形变发生在某特定方向、且处于低形变（形变系数ε≤002 ）区时,电子平均速度v_mean及平均有效质量m^*_mean随形变改变才会很小（相对改变量≤2%）,这意味着此时的碳纳米管低偏压电子输运性能是基本稳定的.而其他形变情形,电子平均速度v_mean或电子平均有效质量m^*_mean或两者随形变变化明显,甚至有跃变,这意味着其低偏压电子输运性能是不稳定的,甚至极不稳定. 关键词： 变形单壁碳纳米管 电子速度 电子有效质量 输运性能稳定性     

Structural, electronic and magnetic properties of the 3d transition metal-doped GaN nanotubes

We have performed first-principles calculations on the structural, electronic and magnetic properties of seven different 3d transition-metal (TM) impurity (V, Cr, Mn, Fe, Co, Ni and Cu) doped armchair (5,0) and zigzag (8,0) gallium nitride nanotubes (GaNNTs). The results show that there is distortion around 3d TM impurities with respect to the pristine GaNNTs for 3d TM-doped (5,5) and (8,0) GaNNTs. The change of total magnetic moment follows Hund’s rule for 3d TM-doped (5,5) and (8,0) GaNNTs, respectively. The total density of states (DOS) indicates that Cr-, Mn-, Fe- and Ni-doped (5,5) GaNNTs as well as Cr-, Mn-, Ni- and Cu-doped (8,0) GaNNTs are all half-metals with 100% spin polarization. The study suggests that such TM-doped nanotubes may be useful in spintronics and nanomagnets.     

A first-principles study of the size-dependent electronic properties of SiC nanotubes

We investigate the structural and electronic properties of SiC nanotubes(NTs) with hexagonal cross sections by a first-principles calculation using plane-wave ultra-soft pseudo-potential technology based on the density-functional theory.Our results reveal that surface-layer C and Si atoms relax significantly upon decreasing the tube-wall thickness because of surface-size and quantum-size effects.We also find that all relaxed SiC NTs stay stably on the nanoscale because of an admixture of sp2 and sp3 hybridization between C and Si atoms and a strong covalent,and that the band gap tends to decrease with increasing tube-wall thickness.Our calculations further indicate that both C and Si atoms on the inner and outer surface of SiC NTs contribute to defect states at the top of the valence band and at the bottom of the conduction band.These results provide reference information for a thorough understanding of the properties of SiC nanostructures and also enable more precise monitoring and control of the growth of SiC nanostructures.     

氮掺杂手性碳纳米管的电子结构和输运特性的理论研究

运用第一性原理的密度泛函理论,结合非平衡格林函数,研究了氮原子取代掺杂手性单壁(6,3)碳纳米管的电子结构和输运特性.计算结果表明:不同构形和不同数目的氮原子取代掺杂对手性碳管的输运性质有很复杂的影响.研究发现,氮原子掺杂明显改变了碳管的电子结构,使金属型手性碳管的输运性能降低,电流-电压曲线呈非线性变化,而且输运性能随着杂质原子间间距的变化而发生显著改变.在一定条件下,金属型碳管向半导体型转变. 关键词： 手性单壁碳纳米管 氮掺杂 电子结构 输运性能     

Theoretical study on the electronic structures and properties of diindolocarbazole isomers

The objective of this work is to provide an in‐depth interpretation of the electronic structures and optical properties of diindolocarbazole isomers. A systematic study of these different structures caused by the linkage pattern was performed via theoretical calculations. The optimized geometries, electronic properties, frontier molecular orbitals, ionization potentials, electron affinities, reorganization energies, and absorption and emission spectra of these isomers have been calculated and analyzed. Based on the detailed comparisons, the diindolocarbazoles act as candidates of different functional materials for optoelectronic application was predicted and the theoretical reference for the synthesis efforts and experimental investigation was provided. Copyright © 2014 John Wiley & Sons, Ltd.     

Correlation of the chemical properties of carbon nanotubes with their atomic and electronic structures

The nature of chemical bonding in carbon nanoclusters is investigated by the PM3 semiempirical quantum-chemical method. The influence of the atomic structure on the electronic characteristics and chemical properties of nanoclusters is analyzed. A σ-π model is proposed for the chemical bonding in nanotubes. It is shown that, in the framework of the proposed model, nanotubes are objects characterized by a small contribution of π states to the valence band top.     

铝氮共掺杂氧化锌纳米管电子结构的第一性原理研究

采用基于密度泛函理论的第一性原理计算, 对(6,0)单壁氧化锌纳米管、铝掺杂、氮掺杂和铝氮共掺杂纳米管的能带结构、态密度和差分电荷密度进行了研究. 结果表明, 氮掺杂可以在纳米管禁带中引入受主能级, 实现纳米管的p型掺杂, 但是受主能级局域性较强, 导致氮溶解度低. 引入铝元素可以有效降低氮形成受主能级局域性, 激活氮元素, 铝氮共掺杂有望成为氧化锌纳米管一种更为有效的p型掺杂方法. 关键词： 氧化锌纳米管 电子结构 共掺杂 第一性原理计算