硼磷掺杂小直径单壁碳纳米管的第一性原理研究

利用基于密度泛函理论的第一性原理计算方法,研究了小直径锯齿形单壁碳纳米管（3,0）的硼（B）、磷（P）单个原子掺杂和B/P共掺杂效应. 计算了B、P单原子掺杂的形成能、能带结构和电子态密度,分析得出B、P掺杂（3,0）单壁碳纳米管是可行的,并且碳纳米管的导电性没有发生明显改变. 本文还计算了在不同掺杂位点,（3,0）金属性碳纳米管的形成能和能带结构,发现B/P共掺杂也是可行的,B和P趋于形成B/P对,并且B/P的掺入使（3,0）金属性碳纳米管的能带打开,由金属性变成半导体性.     

He原子掺杂铝材料的第一性原理研究

采用基于第一性原理的平面波超软赝势方法,结合广义梯度近似(GGA),计算了铝及铝晶胞间隙位置掺入He原子后体系的几何结构、电子结构、总体能量和电荷布居值.计算结果表明:随着氦在金属铝中逐渐形成,铝晶胞体系会发生晶格畸变,但总的趋势是He在铝体系的八面体位置的晶格畸变小于其在四面体位置的晶格畸变.He在铝晶胞八面体和四面体间隙的杂质形成能分别为1.3367 eV和2.4411 eV.由此可知,He在铝晶胞中最稳定位置是八面体间隙位置.同时,文中还从原子尺度层面分析了He原子在铝晶胞中的占位及其键合性质,讨论 关键词： 铝材料 第一性原理 形成能     

Li掺杂对MgH2(001)表面H2分子扩散释放影响的第一性原理研究

本文利用基于密度泛函理论的第一性原理分别研究了MgH₂(001)表面H原子扩散形成H₂分子释放出去的可能路径及金属Li原子掺杂对其影响. 研究结果表明: 干净MgH₂(001)表面第一层释放H原子形成H₂分子有两种可能路径, 其释放能垒分别为2.29和2.50 eV; 当将Li原子替代Mg原子时, 两种H原子扩散释放路径的能垒分别降到了0.31和0.22 eV, 由此表明Li原子掺杂使MgH₂(001)表面H原子扩散形成H₂释放更加容易.     

硼磷掺杂小直径单壁碳纳米管的第一性原理研究简

利用基于密度泛函理论的第一性原理计算方法,研究了小直径锯齿形单壁碳纳米管(3,0)的硼(B)、磷(P)单个原子掺杂和B/P共掺杂效应.计算了B、P单原子掺杂的形成能、能带结构和电子态密度,分析得出B、P掺杂(3,0)单壁碳纳米管是可行的,并且碳纳米管的导电性没有发生明显改变.本文还计算了在不同掺杂位点,(3,0)金属性碳纳米管的形成能和能带结构,发现B/P共掺杂也是可行的,B和P趋于形成B/P对,并且B/P的掺入使(3,0)金属性碳纳米管的能带打开,由金属性变成半导体性.     

B/N掺杂对双层石墨烯电子特性影响的第一性原理研究

利用平面波超软赝势方法研究了B/N原子单掺杂和共掺杂对双层石墨烯电子特性的影响.对掺杂双层石墨烯进行结构优化,并计算了能带结构、态密度、分波态密度等.分析表明,层间范德瓦尔斯相互作用对双层石墨烯的电子特性有比较明显的影响;B/N原子单掺杂分别对应p型和n型掺杂,会使掺杂片层的能带平移,使得体系能带结构产生较大分裂;双层掺杂的石墨烯能带结构与掺杂原子的相对位置和距离有关,对电子特性有明显的调控作用.其中特别有意义的是,B/N双层共掺杂在不同位置情况下会得到金属性或禁带宽度约为0.3 eV的半导体能带.     

Co掺杂BiFeO3的第一性原理研究

采用密度泛函理论结合投影缀加波（PAW）方法,研究了具有钙钛矿结构的BiFeO₃材料及对BiFeO₃进行B位Co元素替代掺杂得到的BiFe_075Co_025O₃材料的磁结构、电子结构、能带结构.结果表明：Co的掺入不破坏原有的钙钛矿结构,对材料铁电性影响不大;掺杂导致原有的G型反铁磁序发生变化,形成了亚铁磁序的磁结构,材料的铁磁性有了很大提高;然而,Co杂质的掺入使材料的绝缘性有所减弱. 关键词： 第一性原理计算 3')" href="#">Co掺杂BiFeO₃ 铁磁性     

In-N共掺杂ZnO第一性原理计算

采用基于密度泛函理论(DFT)的第一性原理平面波超软赝势方法计算了纤锌矿ZnO,N掺杂和In-N共掺杂ZnO晶体的电子结构,分析了N掺杂和In-N共掺杂ZnO晶体的能带结构、电子态密度、差分电荷分布以及H原子对In-N共掺杂ZnO的影响.计算结果表明：N掺杂ZnO在能隙中引入了深受主能级,载流子(空穴)局域于价带顶附近.而加入激活施主In的In-N共掺杂ZnO,受主能级向低能方向移动,形成了浅受主能级.同时,受主能级带变宽、非局域化特征明显、提高了掺杂浓度和系统的稳定性.文章的结论与实验结果相符,从而为实 关键词： 密度泛函理论(DFT) 第一性原理 N掺杂ZnO In-N共掺杂ZnO     

内在缺陷与Cu掺杂共存对ZnO电磁光学性质影响的第一性原理研究

采用基于自旋密度泛函理论的平面波超软赝势方法,研究了Cu掺杂ZnO (简称Cu_(Zn))与内在缺陷共存对ZnO电磁光性质的影响.结果表明,Cu是以替位受主的形式掺入的;制备条件对Cu_(Zn)及内在缺陷的形成起至关重要的作用,富氧条件下Cu掺杂有利于内在缺陷的形成,且Cu_(Zn)-O_i最易形成;相反在缺氧条件下,Cu掺杂不利于内在缺陷的形成.替位Cu的3d电子在价带顶形成未占据受主能级,产生p导电类型.与Cu_(Zn)体系相比,Cu_(Zn)-V_O体系中载流子浓度降低,导电性变差;Cu_(Zn)-V_(Zn)体系中载流子浓度几乎不变,对导电性没影响;Cu_(Zn)-O_i体系中载流子浓度升高,导电性增强.纯ZnO体系无磁性;而Cu掺杂ZnO体系,与Cu原子相连的O原子,电负性越小,键长越短,对磁矩贡献越大;Cu_(Zn)与Cu_(Zn)-O_i体系中的磁矩主要是Cu的3d电子与Z轴上O的2p电子耦合产生的;Cu_(Zn)中存在空位缺陷(V_O,V_(Zn))时,磁矩主要是Cu 3d电子与XY平面内O的2p电子强烈耦合所致;Cu_(Zn)中存在V_(Zn)时,磁性还包含V_(Zn)周围0(5, 6)号原子2p轨道自旋极化的贡献;所有体系中Zn原子自旋对称,不产生磁性.Cu_(Zn)-V_(Zn)和Cu_(Zn)-O_i缺陷能态中,深能级中产生的诱导态是0-0 2s电子相互作用产生的.Cu_(Zn)模型的光学带隙减小,导致吸收边红移;Cu_(Zn)-V_(Zn)模型中吸收和反射都增强,使得透射率降低.     

B掺入Cu∑5晶界间隙位性质的第一性原理研究

本文采用第一性原理方法对清洁Cu∑5晶界与有B掺杂 到间隙位的Cu∑5晶界进 行了拉伸和压缩的模拟研究. 结果分析表明, Cu∑ 5晶界结合因B的掺入得到加强. 清洁Cu∑5晶界处因有较大空隙而存在电子密度低的区域, 晶界结合相对较弱, 在拉伸过程中晶界从其界面处开始断裂. 有B掺杂在间隙位的Cu∑5晶界电子由Cu向Cu-B间积聚, 晶界结合相对较强, 拉伸时晶界从其近邻原子层开始断裂. 在形变小于20%的压缩过程中, B的掺入未对晶界产生明显影响. 关键词： 第一性原理 Cu晶界 B掺杂 拉伸压缩     

B,N协同掺杂金刚石电子结构和光学性质的第一性原理研究

基于金刚石的稳定结构, 在实验研究的基础上, 本文采用基于周期性密度泛函理论计算了B/N单掺杂、共掺杂金刚石的晶体结构, 并就掺杂方式和掺杂后形成能进行了对比研究, 得到了B/N双掺杂的最稳定结构. 在此基础上, 进一步计算了N单掺杂及B/N共掺杂最稳定结构的吸收光谱、电子结构和态密度. 通过与实验结果对比可以看出, 较N单掺杂, B/N共掺杂的吸收光谱发生明显红移, 与实验符合较好. 计算结果表明: N原子单掺杂优先于B原子; 由于原子间的协同作用, B/N近邻共掺杂体系的形成能最低, 为掺杂的最可能结构.     

The low frequency behaviour in high frequency capacitance–voltage characteristics due to contribution of band-to-band tunnelling and generation–recombination in Hg0.75Cd0.25Te MIS capacitors

Hg_1−xCd_xTe Metal–Insulator–Semiconductor (MIS) capacitors were studied both experimentally and theoretically to investigate the capacitance contributions due to band-to-band (btb) tunnelling and generation–recombination (gr) of carriers to inversion layer capacitance. A good fit to the data has been obtained by including the btb contributions rather than gr contributions.     

Electronic properties of graphene nanoribbon doped by boron/nitrogen pair: a first-principles study

By using the first-principles calculations, the electronic properties of graphene nanoribbon (GNR) doped by boron/nitrogen (B/N) bonded pair are investigated. It is found that B/N bonded pair tends to be doped at the edges of GNR and B/N pair doping in GNR is easier to carry out than single B doping and unbonded B/N co-doping in GNR. The electronic structure of GNR doped by B/N pair is very sensitive to doping site besides the ribbon width and chirality. Moreover, B/N pair doping can selectively adjust the energy gap of armchair GNR and can induce the semimetal-semiconductor transmission for zigzag GNR. This fact may lead to a possible method for energy band engineering of GNRs and benefit the design of graphene electronic device.     

Effects of passivation treatment on the surface stability in indium-doped Hg0.8Cd0.2Te epilayers grown on p-Cd0.96Zn0.04Te substrates

Passivation treatment on indium-doped Hg_0.8Cd_0.2Te epitaxial layers grown on p-Cd_0.96Zn_0.04Te substrates by molecular beam epitaxy has been performed in order to improve the surface stability of the Hg_0.8Cd_0.2Te layers. Room-temperature capacitance–voltage measurements clearly revealed metal-insulator–semiconductor (MIS) behavior for the Al/ZnS/passivated Hg_0.8Cd_0.2Te layer/Cd_0.96Zn_0.04Te diodes. The fast state density and the fixed charge density of the Al/ZnS/passivated Hg_0.8Cd_0.2Te/Cd_0.96Zn_0.04Te diode with a sulfur-treated Hg_0.8Cd_0.2Te layer were smaller than those with a chemically oxidized Hg_0.8Cd_0.2Te layer. The interface state density at the ZnS/sulfur-treated Hg_0.8Cd_0.2Te interface were low at 10¹¹ eV⁻¹ cm⁻² at the middle of the Hg_0.8Cd_0.2Te energy gap. These results indicate that the Hg_0.8Cd_0.2Te epilayer is significantly passivated by sulfur treatment and that the passivated Hg_0.8Cd_0.2Te layers can be used for Hg_1−xCd_xTe-based MIS diodes and MIS field-effect transistors.     

带有碳杂质的钨中氢稳定性的第一性原理研究

应用第一性原理计算方法研究了碳(C)原子对钨(W)中氢(H)原子稳定性的影响. 本征W中, 当C-H间距离为～2.5 Å时, H的溶解能出现最低值, 此时为H最稳定的位置. W中存在空位时, 由于C的影响, H占据的最佳电子密度面值为0.10 Å^-3. 研究发现, W中单空位最多能容纳10个H原子, 且不能形成H分子, 不同于没有C存在的情况, 表明C对W中H稳定性存在很大影响. 此外, 当两个C原子存在于空位中时, H占据的最佳电子密度面值变为0.13 Å^-3.     

Hydrogen storage of Mg1-xMxH2 (M=Ti, V, Fe) studied using first-principles calculations

In this work, the hydrogen storage properties of the Mg-based hydrides, i.e., Mg_1-xM_xH₂ (M=Ti, V, Fe, 0 ≤ x ≤ 0.1), are studied using the Korringa-Kohn-Rostoker (KKR) calculation with the coherent potential approximation (CPA) approximation. In particular, the nature and the concentrations of the alloying elements and their effects are studied. Moreover, the material's stability and hydrogen storage thermodynamic properties are discussed. In particular, we find that the stability and the temperature of desorption decrease without significantly affecting the storage capacities.     

Boron/nitrogen pairs Co-doping in metallic carbon nanotubes: a first-principle study

By using the first-principles calculations, the electronic structure and quantum transport properties of metallic carbon nanotubes with B/N pairs co-doping have been investigated. It is shown that the total energies of metallic carbon nanotubes are sensitive to the doping sites of the B/N pairs. The energy gaps of the doped metallic carbon nanotubes decrease with decreasing the concentration of the B/N pair not only along the tube axis but also around the tube. Moreover, the I--V characteristics and transmissions of the doped tubes are studied. Our results reveal that the conducting ability of the doped tube decreases with increasing the concentrations of the B/N pairs due to symmetry breaking of the system. This fact opens a new way to modulate band structures of metallic carbon nanotubes by doping B/N pair with suitable concentration and the novel characteristics are potentially useful in future applications.     

First-principles study of metallic carbon nanotubes with boron/nitrogen co-doping

Using the first-principles calculations, we investigate the electronic band structure and the quantum transport properties of metallic carbon nanotubes (MCNTs) with B/N pair co-doping. The results about formation energy show that the B/N pair co-doping configuration is a most stable structure. We find that the electronic structure and the transport properties are very sensitive to the doping concentration of the B/N pairs in MCNTs, where the energy gaps increase with doping concentration increasing both along the tube axis and around the tube, because the mirror symmetry of MCNT is broken by doping B/N pairs. In addition, we discuss conductance dips of the transmission spectrum of doped MCNTs. These unconventional doping effects could be used to design novel nanoelectronic devices.     

A study on strain affecting electronic structures and optical properties of wurtzite Mg0.25 Zn0.75O by first-principles

We have made a first principles study to investigate density of states, band structure, the dielectric function and absorption spectra of wurtzite Mg 0.25 Zn 0.75 O. The calculation is carried out in a-axis and c-axis strain changing in the range from 0.3 to -0.2 in intervals of 0.1. The results calculated from density of states show that the bottom of conduction band is always dominated by Zn 4s and the top of valence band is always dominated by O 2p in a-axis and c-axis strain. Zn 4s will shift to higher energy range when a-axis strain changes in the range from 0.3 to 0, and then shift to lower energy range when a-axis strain changes in the range from 0 to -0.2. But Zn 4s will always shift to higher energy range when c-axis strain changes in the range from 0.3 to -0.2. The variations of band gap calculated from band structure and absorption spectra are also investigated, which are consistent with the results obtained from density of states. In addition, we analyse and discuss the imaginary part of the dielectric function ε 2 .     

Pd掺杂对NiTi合金马氏体相变和热滞影响的第一性原理研究

一定浓度的Pd掺杂能够有效地提高Ni Ti合金的相变温度,并且降低热滞.为了解其作用机理,采用第一性原理计算方法,对不同Pd掺杂浓度下Ni Ti合金(Ni24-n Pd n Ti24,n=2,3,4,5,6,9,12;掺杂浓度分别为4.2 at.%,6.3 at.%,8.4 at.%,10.4 at.%,12.5 at.%,18.8 at.%,25 at.%)的相稳定性和结构特性进行计算讨论.马氏体相变温度可以通过奥氏体与马氏体两相能量差值进行分析,且能量差越大相变温度越高;相变过程中两相晶格常数之比越接近于1则热滞越接近于0.计算结果表明:当掺杂浓度小于10.4 at.%时,B19′是最稳定的马氏体相,体心四方(BCT)结构与B19′相的能量差随掺杂浓度的增加略有下降;当掺杂浓度大于等于10.4 at.%时,B19相是最稳定的马氏体相,BCT与B19的能量差随着掺杂浓度增加显著升高.这意味着在掺杂浓度大于等于10.4 at.%时相变温度随掺杂浓度的增加而显著增加.用几何模型分析了马氏体相变的热滞,结果表明掺杂浓度为10.4 at.%时B2到B19相的相变过程热滞最小,与实验结果一致.     

Dissociations of O2 molecules on ultrathin Pb(111) films: first-principles plane wave calculations

Using first-principles calculations, we systematically study the dissociations of O₂ molecules on different ultrathin Pb(111) films. According to our previous work revealing the molecular adsorption precursor states for O₂, we further explore why there are two nearly degenerate adsorption states on Pb(111) ultrathin films, but no precursor adsorption states existing at all on Mg(0001) and Al(111) surfaces. The reason is concluded to be the different surface electronic structures. For the O₂ dissociation, we consider both the reaction channels from gas-like and molecularly adsorbed O₂ molecules. We find that the energy barrier for O₂ dissociation from the molecular adsorption precursor states is always smaller than that from O₂ gas. The most energetically favorable dissociation process is found to be the same on different Pb(111) films, and the energy barriers are found to be influenced by the quantum size effects of Pb(111) films.