高压下ZnSe的电子结构和光学性质

运用密度泛函理论体系下的平面波赝势(PWP)和广义梯度近似(GGA)方法,利用第一性原理计算了不同的压强下ZnSe晶体闪锌矿结构,得到了它的平衡晶格常数、总能量、电子态密度分布、能带结构、光反射与吸收系数等性质,详细讨论了高压下ZnSe的电子结构,并且结合实验结果定性地分析了高压下的光学性质. 关键词： 闪锌矿结构 态密度 能带结构 密度泛函理论     

闪锌矿GaN弹性性质、电子结构和光学性质外压力效应的理论研究

采用基于密度泛函理论(DFT)的第一性原理平面波赝势方法,结合广义梯度近似(GGA)下的RPBE和局域密度近似(LDA)的CA-PZ交换-关联泛函对闪锌矿结构的GaN在高压的性质进行了系统研究. 计算结果表明:弹性常数、体模量、杨氏模量和能隙都具有明显的外压力效应,计算结果与实验值和理论值很好的符合. 同时利用计算的能带结构和态密度系统分析了GaN的介电函数、折射率、反射率、吸收系数和能量损失函数等光学性质及其外压力效应. 分析结果为GaN的设计与应用提供了理论依据. 关键词： 第一性原理计算 电子结构 光学性质 闪锌矿GaN     

高压下固态Kr弹性性质、电子结构和光学性质的第一性原理计算

采用密度泛函理论中平面波基矢,模守恒赝势结合局域密度近似以及广义梯度近似对固态Kr在高压下的结构以及弹性性质进行了研究, 通过计算发现弹性常数,Debye温度以及声速都随压力的增大而增大,所计算的弹性常数与实验和其他的理论符合的很好. 利用Debye模型得到了固态Kr的热力学性质, 熵随压力的增大而减小,随温度升高而升高;而定容热容C_v,定压热容C_p则随温度升高而升高,而且C_v在达到一定温度时趋于定值,所得的热力学性质和实验值是相符的．最后还预测了固态Kr在高压下的电子结构和光学性质, 计算结果表明随压力的增加固态Kr的前沿能带变窄,光吸收系数增大,吸收峰增宽,电子更容易发生跃迁,固态Kr有可能转化为半导体． 关键词： Kr 第一性原理 弹性常数 光学性质     

闪锌矿结构的PtN:一种不稳定的过渡金属氮化物

基于密度泛函理论的第一性原理的赝势方法，采用局域密度近似和广义梯度近似，研究了闪 锌矿结构的PtN晶体的电子结构和力学稳定性.结果表明具有闪锌矿结构的PtN是一种力学不 稳定的金属氮化物，岩盐矿结构PtN的聚合能略大于闪锌矿结构PtN的聚合能，在适当压力条 件下可以发生从闪锌矿到岩盐矿的相变. 关键词： PtN 电子结构 力学稳定性 第一原理计算     

反位缺陷对碳化硅纳米管电子结构和光学性质影响研究

采用基于密度泛函理论的第一性原理计算对含有反位缺陷（5,5）单壁碳化硅纳米管的电子结构和光学性质进行了研究.纳米管进行结构优化的结果显示,C_Si缺陷在纳米管表面形成了凹陷,Si_C缺陷形成了凸起;反位缺陷在纳米管的导带底附近形成了缺陷能级,使纳米管表现出n型导电的特点,由价带顶到缺陷能级的跃迁,在垂直和平行于纳米管管轴方向上形成了新的介电峰.     

TiO$lt;sub$gt;2$lt;/sub$gt;纳米管电子结构和光学性质的第一性原理研究

运用基于密度泛函理论的第一性原理方法, 系统研究了小尺寸锐钛矿相(n,0)型TiO₂纳米管(D<16 Å)的几何构型、电子结构和光学性质. 结果表明: 随着管径增大, 体系单位TiO₂分子的形成能降低, 体系趋于稳定; 在管径14 Å左右, (n,0)型TiO₂纳米管会发生一次构型的转变. 能带分析显示, TiO₂纳米管的电子态比较局域化, 小管径下(D<14 Å)其导电性更好; 随着构型的转变, TiO₂纳米管由直接带隙转变为间接带隙, 并且带隙值随着管径的增大而增大, 这是由于π轨道重叠效应的影响大于量子限域效应所导致的结果. 两种效应的竞争, 使得TiO₂纳米管的介电函数虚部ε₂ (ω)谱的峰值位置随管径增大既可能红移也可能蓝移, 管径大于9 Å (即(8, 0)管)之后, TiO₂纳米管的光吸收会出现明显的增强. 关键词： 2纳米管')" href="#">TiO₂纳米管 第一性原理 电子结构 光学性质     

高压下ZnS的电子结构和性质

运用密度泛函理论体系下的平面波赝势(PWP)和广义梯度近似(GGA)方法，计算研究了闪锌矿结构的ZnS晶体在不同的外界压强下的电子结构. 通过分析发现，随着外界压强的增大，晶格常数和键长在不断缩小，从S原子向Zn原子转移的电荷越来越少，Zn—S键的共价性逐渐增强，Zn原子和S原子的态密度都有不同程度的变化，而且还有向低能量移动的趋势. 当外界压强达到24GPA时，ZnS从直接带隙半导体变成间接带隙半导体，而且随着压强的增大，间接带隙逐渐变小，直接带隙逐渐增大. 关键词： 闪锌矿结构 态密度 能带结构 密度泛函理论     

高压下闪锌矿InN光电性质的密度泛函研究

 采用密度泛函理论,计算了闪锌矿型InN在压力下的结构、力学性质和光学性质,结果显示,随着压强的增大晶格常数减小。给出了零压下C₁₁、C₁₂、B、C_s、C₄₄的值及至70 GPa压力下弹性常数随压强的变化关系。结果表明,C₁₁、C₁₂、B随压强增大而增大,C_s、C₄₄随压强增大而减小,计算结果与现有实验和理论结果符合较好。在价带区,InN的分态密度（PDOS）有两个带,且在费米面附近密度很小,显示其倾向于形成稳定结构并且导电性较差。对闪锌矿型InN在高压下的光学性质研究发现,导带电子向高能方向偏移,而价带电子向低能方向偏移,结果导致能带间隙增大,光吸收谱在压力的作用发生了“蓝移”。研究结果对认识高压下闪锌矿型InN的结构、电学及光学性质具有重要意义。     

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.     

第一性原理研究电场对BN纳米管电子结构的影响

采用基于密度泛函理论的第一性原理计算研究了电场对BN纳米管的电子结构的影响.首先对在不同电场强度下的纳米管几何结构进行了优化,可以看出纳米管沿轴方向层间距出现了不规则的变化.电子能带结构显示,在电场作用下,zigzag型和armchair型两种结构纳米管的能带向低能方向移动,并且导致纳米管的带隙有显著的减小.电场使得armchair型纳米管的带隙发生了从间接带隙向直接带隙的转变.在电场作用下,纳米管的两端态密度呈现出明显的差异,正负电荷沿轴向出现了沿轴向的空间分离,Mulliken电荷分布图揭示出最高占据轨道和最低未占据轨道分居在纳米管的两端.     

Electronic,structural, and thermal properties of a nanocable consisting of carbon and BN nanotubes

The band structure and thermal behavior of a coaxial C/BN nanocable (5,5)C@(17,0)BN consisting of a carbon nanotube and a boron nitride nanotube have been studied using a tight-binding approximation based on density functional theory. The system is stable up to T～3500–3700 K. As the temperature increases, deformations of the BN tube begin earlier than those of the carbon tube. The near-Fermi states of the nanocable are formed by the overlapping π-π* bands of the carbon tube, and the outer BN nanotube (the nanocable sheath) is an insulator with a bandgap of ～4 eV. The electronic properties of the nanocable (the metallic-type conductivity of the C tube and the insulating character of the BN tube) are retained over the entire temperature interval.     

Structural and electronic properties of carbon nanotubes under hydrostatic pressures

We studied the structural and electronic properties of carbon nanotubes under hydrostatic pressures based on molecular dynamics simulations and first principles band structure calculations. It is found that carbon nanotubes experience a hard-to-soft transition as external pressure increases. The bulk modulus of soft phase is two orders of magnitude smaller than that of hard phase. The band structure calculations show that band gap of (10, 0) nanotube increases with the increase of pressure at low pressures. Above a critical pressure (5.70GPa), band gap of (10, 0) nanotube drops rapidly and becomes zero at 6.62GPa. Moreover, the calculated charge density shows that a large pressure can induce an {sp}²-to-{sp}³ bonding transition, which is confirmed by recent experiments on deformed carbon nanotubes.     

Electronic structure of SiC/BN composite segmented nanotubes

The electronic structure of segmented nanotubes composed of the alternating layers of (5,5) and (9,0) BN and SiC nanotubes in armchair and zigzag configurations, which differed in the orientation of the chemical bonds in the segments and the nature of the bonds (Si-N and B-C or Si-B and N-C) at the boundaries of BN and SiC regions, has been calculated using the linearized augmented cylindrical wave method. The calculations have been performed using the local density functional and the muffin-tin approximation for the electronic potential. It has been found that depending on the bonds at the segment boundaries, the (5,5) BN/SiC nanotubes are semiconductors with the energy gap E _g of 1 to 3 eV, whereas the (9,0) BN/SiC nanotubes exhibited a metal, semimetal, or semiconductor (E _g ～ 1 eV) type of band structures.     

Adsorption of mercaptopurine drug on the BN nanotube,nanosheet and nanocluster: a density functional theory study

ABSTRACT

We have investigated the interaction of mercaptopurine (MP) drug with BN nanotube, nanosheet and nanocluster using density functional theory calculations in the gas phase, and aqueous solution. We predicted that the MP drug tends to be physically adsorbed on the surface of BN nanosheet with an adsorption energy (E_ad) about ?3.2?kcal/mol. The electronic properties of BN nanosheet are not affected by the MP drug, and this sheet is not a sensor. But the electronic properties of BN nanotube and nanocluster are significantly sensitive to this drug in both gas phase, and aqueous solution. The BN nanocluster suffers from a long recovery time (8.8?×?10⁸?s) because of a strong interaction (E_ad?=??28.6?kcal/mol), and this cluster is not a proper sensor for MP detection. But the BN nanotube benefits from a short recovery time about 49.5?s at room temperature, and may be a promising candidate for application in the MP sensors. The water solvent decreases the strength of interaction between the BN nanotube, and MP drug, but it does not affect the electronic sensitivity of the nanotube sensibly.     

GGA-based analysis of the metformin adsorption on BN nanotubes

Density functional theory (DFT) studies are done to investigate structural and electronic properties of (5,5) chirality single walls boron nitride nanotubes (BNNTs) in the armchair model interacting with metformin (MF) on the surface and ends. Our calculations consider the exchange-correlation energies with the Hamprecht–Cohen–Tozer–Handy functional within the generalized gradient approximation (HCTH-GGA) and the double polarized DNP base function. The geometry optimization follows the minimum energy criterion for all six geometries we have considered. Results show that the MF is adsorbed through the groups NH₂–NH at one end of the nanotube. The system polarity is increased which indicates the possible dispersion and solubility. Moreover the interaction between these species induces an increase in the chemical reactivity of the order of 0.42 eV. Meanwhile the solvation in water keeps the semiconductor characteristics of both nanotube and MF. The work function of the BNNT-MF is drastically reduced respect to the pristine system when the BN nanotube is doped at its surface and ends with carbon. This means that the functionalized BN nanotube facilitates conditions to improve field emission.     

钴修饰氮化铝纳米管的储氢性能

本文采用密度泛函理论中的广义梯度近似系统地研究了钴原子修饰的(5,5)单壁氮化铝纳米管(SWANNT)的几何结构、电子性质以及储氢性能.研究结果表明:钴原子倾向于以顶位的形式吸附于(5,5) SWANNT表面N原子上.在钴原子周围可以吸附4个完整的H分子,平均吸附能为0.624 e V,表明钴原子修饰的SWANNT材料有望在温和环境中实现对H分子的快速吸附和脱附.     

Influence of isoelectronic impurities on the electronic structure of BN nanotubes

Via the example of a (5, 5) boron-nitrogen armchair nanotube, the influence of isoelectronic substitutional impurities on the electronic structure of BN nanotubes has been investigated with the use of linear augmented cylindrical waves. The treatment is based on the local density approximation and the muffin-tin approximation for the electron potential. In this method, the electronic spectrum of a system is governed by the free motion of electrons in the interatomic space between cylindrical barriers and the electron scattering on atomic centers. It has been found that the substitution of one atom of N by P leads to the splitting of all twofold degenerate bands by 0.2 eV on average, a decrease in the energy gap from 3.5 to 2.8 eV, the separation of the s(P) band from the high-energy region of the s(B, N) band, as well as to the formation of the impurity π(P) and π*(P) bands, which form the valence-band top and conduction-band bottom in the doped system. The influence of an As atom on the electronic structure of (5, 5) BN nanotubes is qualitatively similar to the case of phosphorus, but the energy gap is smaller by 0.5 eV. The optical gap in the nanotubes is closed due to the effect of the Sb atom impurity. A substitution of one B atom by an Al atom results in the strong perturbation of the band structure and the energy gap in this case is only 1.6 eV in contrast to the weak indium-induced perturbation of the band structure of the BN nanotube. In the latter case, the energy gap is 2.9 eV. The above effects can be detected by the optical and photoelectron spectroscopy methods, as well as by measuring the electrical properties of the nanotubes. They can be used to create electronic devices based on boron-nitrogen nanotubes.     

Theoretical study on the effect of dopant positions and dopant density on transport properties of a BN co-doped SiC nanotube

We investigate the effect of dopant (boron ‘B’–nitrogen ‘N’) position and density on electronic transport properties of a BN co-doped silicon carbide nanotube (SiCNT). The results show an increase in conductance when both BN impurities are far in space from each other. Orbital delocalization and appearance of new electronic states around Fermi level contribute to the current when this spacing is increased. On the other hand, a reduction in SiCNT conductivity was observed when BN dopant density was increased. This is attributed to the electronic states moving away from the Fermi level and orbital localization at higher bias voltages.     

高压下三元金属间化合物SrAlSi的电学和晶格动力学特性

基于密度泛函理论的第一性原理方法,系统研究了三元金属间化合物SrAlSi在高压下的电子性质和晶格动力学性质.三元金属间化合物SrAlSi具有和MgB₂类似的六角蜂巢状结构,Sr原子取代了Mg原子的位置,Al、Si原子无序地占据B原子的位子.通过对SrAlSi三元金属间化合物能带和三维费米面的计算,发现在压力的作用下SrAlSi费米面附近的能带发生电子拓扑变化,压力可以导致电子拓扑结构相变(ETTs).通过晶格动力学研究发现,在压力的作用下,SrAlSi的光学支沿着A-L-H方向逐渐软化,声学支逐渐变硬,说明金属间化合物SrAlSi在压力作用下结构不是很稳定,随着压力的继续增大,会有新的结构出现.