Zr基大块非晶中添加元素对非晶形成能力及耐蚀性的影响

运用实空间递归方法研究了添加元素Nb,Ta,Y,La对Zr基非晶合金的非晶形成能力和耐腐蚀性能的影响.用计算机编程构造了Zr基非晶中初始晶化相Zr₂Ni的原子结构模型,用Zr₂Ni中的二十面体原子团簇模拟非晶中的二十面体团簇.计算了替代二十面体中心或顶角位置原子前后Ni,Zr及合金元素的局域态密度、团簇中心Ni与近邻Zr原子及Ni与替代元素Nb,Ta,Y,La间的键级积分,还计算了合金元素替代前后团簇的费米能级.局域态密度计算结果表明：合金元素Cu占据二十面体团 关键词： 电子结构 Zr基大块非晶 非晶形成能力 耐蚀性     

NiZr,AlZr和BCr相局域原子短程序特征

晶体和非晶合金具有以近邻多面体团簇为特征的微结构,这些团簇包含有形成其母相的空间局域原子短程序结构信息.本文正是从局域原子团簇特征出发,详细分析了传统晶体相描述中具有相同结构的NiZr,AlZr和BCr相,结果表明它们却具有不同的局域原子特征.这种不同可能是由单胞大小及原子占位略有不同造成的.由于这种不同于传统的晶体学描述方法给出了微观结构特点,对晶体相的重新认知及材料设计会大有帮助.     

La65X35(X=Ni,Al)非晶合金原子结构的第一性原理研究

运用基于密度泛函理论的第一性原理分子动力学和静态电子结构计算,研究了La₆₅X₃₅（X=Ni,Al）非晶合金体系原子结构随温度演化的规律及其相关电子结构特性.使用径向分布函数、Voronoi团簇以及键对分析等给出了从高温液体快速冷却到玻璃态过程中原子结构的演化规律.研究发现,该类合金体系的原子排布符合局域密堆模型,两体系中占比最大的特征多面体类型由溶质与溶剂原子半径比调控;两体系中高五次对称性局域结构随温度的下降而增加验证了其在抑制晶化方面的重要作用;利用投影态密度分析两体系电子结构之间的差异,指出La-5d与Ni-3d电子间强烈的杂化是La–Ni 间键长缩短的电子结构起源,为理解成分相关的结构和物性提供了重要线索.     

递归方法和团簇磁性的计算

介绍了如何应用递归方法将哈密顿矩阵三对角化,从而求得局域态密度 ,并以计算铑团簇的磁矩为例,说明了递归方法在研究团簇的电子结构方面的应用。     

YnN(n=2-12)团簇的结构与性质研究

在密度泛函理论框架下,用广义梯度近似（GGA）的方法研究YnN（n=2-12）团簇的电子结构,系统计算了它们的基态束缚能Be（eV）、最高占据轨道（HOMO）与最低未占据轨道（LUMO）之间的能隙、二阶能量差分 (au)、离解能 (au)、团簇的总磁矩Mt（ ）,最近邻N原子的Y原子所带的局域电荷QY（C）和磁矩MY（ ）、掺杂原子N所带的局域电荷QN（C）和磁矩MN（ ）。研究表明,Y6N、Y8N、Y10N的基态具有较高稳定性;对于YnN（n=2-12）的所有团簇,电荷总是由Y原子转移到N原子,YnN（n=2-12）团簇中Y—N表现为离子键的性质;当n=3,4,5,9,10,11,12时,团簇的磁矩为零,团簇的磁性消失,当n=2,6,7,8时,团簇具有磁性,其中n=6时,团簇的磁性最强。     

链间耦合对聚乙炔多链体系中电子极化子再激发态的影响

从拓展紧束缚模型出发,研究了链间耦合对反式聚乙炔多链体系中电子极化子再激发态的晶格位形、净电荷密度、局域能级波函数和态密度的影响。结果发现：对于两条链体系,当链间耦合很小（eV）时,注入到系统中的电子只会在第一条链上诱发产生一个晶格缺陷,形成电子极化子再激发态,这和单链体系是一致,而第二条链仍是二聚化基态。随着链间耦合的增大,第一条链上缺陷的局域度减少而第二条链上的缺陷局域度相应增加,直至两条链上的位形相同。对于多条链（5条链和6条链）体系,当耦合很小（0.05eV）时,电子极化子再激发态也只会存在于一条链上,当链间耦合较强时,极化子再激发态会在链间层次性地扩展开来,并不会出现多条链位形相同。从两条链的能级图上可以看到随着链间耦合的增大,体系的带隙不断的增大和电子态密度显示的是完全吻合的,体系的导电性减弱。通过分析两条链体系在eV和eV的能级态密度,发现链间耦合越强,则中间局域能级的态密度越小,最后没有中间局域态。     

(CoMn)n(n=1~5)合金团簇的结构和磁性

采用密度泛函理论中的局域自旋密度近似和广义梯度近似对(CoMn)n(n=1～5)团簇的几何构型进行优化、能量、频率和磁性计算,确定了团簇的基态,对其基态的磁性和电子结构进行了系统研究,并与相对应的一元团簇进行了结构和磁性比较.研究表明,两种方法确定的基态构型基本一致,当n=1～4时,等比CoMn二元合金团簇的几何形状仍与一元团簇相同;(CoMn)3和(CoMn)4团簇出现了磁性双稳态,显示铁磁性和反铁磁性耦合;二元CoMn合金团簇中Co、Mn原子磁性仍能保持一元Co、Mn团簇基态的磁性.     

飞秒激光与D2气体团簇的相互作用

原子（分子）团簇是有几个到几千乃至几万个原子（分子）通过物理或化学结合力形成的相对稳定的微观集合体，是介于原子分子和宏观固体物质之间的一种特殊的过渡物质结构。原子团簇尺寸比激光波长短，与强激光相互作用比原子或小分子更为激烈。团簇能够吸收相当大部分的激光能量，并产生超热电子和高电荷态的离子，高电荷态的离子会激发辐射出光子。     

Al12N、Al12B团簇结构和电子性质的密度泛函计算

利用密度泛函理论研究了Al12N和Al12B团簇的原子结构和电子性质,通过各种异构体的比较,发现两种掺杂团簇的最低能量结构都是完好的二十面体(Ih)结构,N(B)原子占据在二十面体的中心.高对称性团簇形成稀疏离散的电子态密度和大的电子能隙.在Al-N之间发生较大的电荷转移.因此我们建议把Al12N团簇看作是碱金属超原子,Al12B团簇看作是卤素超原子,用来构造团簇组装固体.     

Pd对Ti合金钝化影响的电子理论研究

采用递归法计算了Ti合金的电子态密度、环境敏感镶嵌能、费米能级等电子结构参量.计算发现Pd在晶体体内比在其表面的环境敏感镶嵌能高,说明Pd易于在 Ti合金表面偏聚.Pd在表面时,原子团簇形成能为负值,说明Pd以团簇形式分布于合金表面.态密度计算结果表明,Pd的局域态密度局限在很窄的能量范围内(-20—-15 eV),使Ti合金的总态密度在此区出现尖峰.该尖峰的存在降低了Ti合金的费米能级,于是表面含Pd较多的区域费米能级较低,含Pd少或不含Pd的区域费米能级较高.费米能级不同的两区域接触会形成微电池,在腐 关键词： Ti合金 钝化 电子结构 表面     

Be掺杂纤锌矿ZnO电子结构的第一性原理研究

采用密度泛函理论结合投影缀加波方法,对Be掺杂导致ZnO禁带宽度增加的机理进行了研究.通过对掺杂前后电子能带结构、总态密度以及分态密度的计算和比较,发现导带底(CBM)是由Be 2s电子与Zn 4s电子共同控制;而Be_xZn_1-xO价带顶 (VBM)始终由O 2p电子占据.随着掺杂量的增加,决定带隙宽度的CBM的位置上升,同时VBM的位置下降,从而导致了带隙的变宽,出现了蓝移现象.此外,Be掺杂会使晶胞发生压缩,这种压应变也是导致Be 关键词： 密度泛函理论 电子结构 Be掺杂ZnO     

Valence band formation in small silver clusters

UV photoemission spectra of valence electrons in small silver clusters have been compared with spectra from bulk silver samples using synchrotron radiation, 16 <hν< 27 eV. Spectra for single silver atoms supported on carbon are indicative of a completely filled 4d¹⁰ initial state configuration. With increased cluster size, both density of states and valence band modulations with respect to photon energy resemble the bulk metal more closely. Spectral modulation, characteristic of conservation of crystal momentum, appears to require a cluster consisting of ～150 atoms.     

Electron states in metal clusters

Radiative transitions in metal clusters are analyzed in terms of quantum transitions of valence electrons that interact with surrounding valence electrons and ion cores. The analysis is based on the solution of the Thomas-Fermi equation for valence electrons in a spherical cluster. The quantum states of valence electrons and the energy and the dipole moments of transitions are determined in the quasiclassical approximation. It is shown that the frequencies of dipole oscillations and the dipole moments of the transitions strongly depend on the size of a cluster.     

Optical studies on the red luminescence of InGaN epilayers

Photoluminescence, photoluminescence excitation and time-resolved photoluminescence studies were performed in a partially relaxed InGaN epilayer, and exhibiting a 3D growth mode at the surface. Two emission bands, a red (centred at 1.88 eV) and a blue (centred at 2.58 eV) were observed. In order to investigate their origin and their relation with the strain relaxation along the growth direction, the sample was etched. After etching, only an asymmetrical broad emission band centred at 2.15 eV was observed.The decrease of decay time and the increase of the band edge absorption energy with increasing monitored photon energy, along the red emission, are assigned to the effect of localization of excitons at potential minima, originated in compositional and strain inhomogeneities of the sample. Therefore, the blue shift observed on this band with an increase in temperature, is caused by the population of higher energy states. The large difference between the luminescence intensities, decay times and the thermal quenching of the red and blue (centred at 2.58 eV) band is also accounted for by the localization model. It is demonstrated that the luminescence observed after etching is a superposition of two bands, one originated from the InGaN film, and the other from the GaN underlayer. The large difference between absorption and emission energies, compared with those measured in the as-grown sample, within the same spectral region, indicates that this emission has a different origin. It is suggested that deep levels might be responsible for the luminescence observed after etching.     

Alloy model for high-temperature superconductors

An alloy model is proposed for the electronic structure of high-temperature superconductors. It is based on the assumption that holes and extra electrons are localized in small copper-oxygen clusters, that would be the components of such an alloy. This model, when used together with quantum chemical calculations on small clusters, can explain the structure observed in the experimental densities of states of both hole and electron superconductors close to the Fermi energy. The main point is the strong dependence of the energy level distribution and composition on the number of electrons in a cluster. The alloy model also suggests a way to correlate T_c with the number of holes, or extra electrons, and the number of adequate clusters to locate them.     

Intraband radioluminescence of LiF crystals

Spectra of high-energy electrons are calculated in the electron-hole ionization-passive region of lithium fluoride crystals for the conditions of intense irradiation by short pulses of accelerated electrons. The yield of intraband radioluminescence of these crystals is estimated in comparison with the yield of this kind of luminescence of more extensively studied NaCl crystals. The calculations demonstrate that the yield of radioluminescence determined by electron transitions in the conduction band of LiF crystals is two orders of magnitude weaker than the yield of analogous luminescence of NaCl crystals. This is explained, first, by special features of the energy band structure and, second, by the form of the energy dependence of the density of states in the conduction band of LiF crystals. The yield of hole-type intraband radioluminescence is estimated for various assumed relations between the widths of the valence and the forbidden bands.     

Uniaxial strain-modulated electronic structures of CdX (X = S,Se, Te) from first-principles calculations:A comparison between bulk and nanowires

Using first-principles calculations based on density functional theory, we systematically study the structural deformation and electronic properties of wurtzite CdX(X = S, Se, Te) bulk and nanowires(NWs) under uniaxial [0001] strain. Due to the intrinsic shrinking strain induced by surface contraction, large NWs with {10ˉ10} facets have heavy hole(HH)-like valence band maximum(VBM) states, while NWs with {11ˉ20} facets have crystal hole(CH)-like VBM states. The external uniaxial strain induces an HH–CH band crossing at a critical strain for both bulk and NWs, resulting in nonlinear variations in band gap and hole effective mass at VBM. Unlike the bulk phase, the critical strain of NWs highly depends on the character of the VBM state in the unstrained case, which is closely related to the size and facet of NWs. The critical strain of bulk is at compressive range, while the critical strain of NWs with HH-like and CH-like VBM appears at compressive and tensile strain, respectively. Due to the HH–CH band crossing, the charge distribution of the VBM state in NWs can also be tuned by the external uniaxial strain. Despite the complication of the VBM state, the electron effective mass at conduction band minimum(CBM) of NWs shows a linear relation with the CBM–HH energy difference, the same as the bulk material.     

Electronic structures and energy band properties of Be- and S-doped wurtzite ZnO

The energy band properties, density of states, and band alignment of the BexZn1-xO1-ySy alloy （Be- and S-doped wurtzite ZnO） are investigated by the first-principles method. BexZn1-xO1-ySy alloy is a direct band gap semiconductor, the valence band maximum （VBM） and the conduction band minimum （CBM） of BexZn1-xO1-ySy are dominated by S 3p and Zn 4s states, respectively. The band gap and lattice constant of BexZn1-xO1-ySy alloy can be modulated by changing the doped content values x and y. With the increase in Be content value x in the BexZnl-xOl-ySy alloy, the band gap increases and the lattice constant reduces, but the situation is just the opposite when increasing the S content value y in the BexZn1-xO1-ySy alloy. Because the lattice constant of Be0.375Zn0.625O0.75S0.25 alloy is well matched with that of ZnO and its energy gap is large compared with that of ZnO, so the Be0.375Zn0.625O0.75S0.25 alloy is suitable for serving as the blocking material for a high-quality ZnO-based device.     

垒层厚度对InGaN/GaN多量子阱电注入发光性能的影响及机理

研究了不同垒厚对InGaN/GaN多量子阱电注入发光性能的影响及机理。实验发现,当GaN垒层的厚度从6 nm增大到24 nm时,垒厚的样品发光强度更强,而且当注入电流增加时,适当增加垒厚,可以更显著增加发光强度。进一步结合发光峰位和光谱宽度的研究表明,由于应力和极化效应的存在,当垒层厚度在6~24 nm范围内时,适当增加垒层厚度不仅会使得能带的倾斜加剧,减少电子泄露,而且也会增加InGaN阱层的局域态深度,从而改善量子阱的发光性能。     

First-principles energy band calculation for undoped and N-doped InTaO4 with layered wolframite-type structure

The electronic structures of undoped and N-doped InTaO₄ with optimized structures are calculated within the framework of the density functional theory. Calculated lattice constants are in excellent agreement with experimental values, within a difference of 2%. The valence band maximum (VBM) is located near the middle point on the ZD line and the conduction band minimum (CBM) near the middle point on the DX line. This means that InTaO₄ is an indirect-gap material and a minimum theoretical gap between VBM and CBM is ca. 3.7 eV. The valence band in the range from −6.0 to 0 eV mainly consists of O 2p orbitals, where In 4d5s5p and Ta 5d orbitals are slightly hybridized with O 2p orbitals. On the other hand, the conduction band below 5.5 eV is mainly composed of the Ta 5d orbitals and the contributions of In and O orbitals are small. The band gap of N-doped InTaO₄ decreases by 0.3 eV than that of undoped InTaO₄, because new gap states originating from N 2p orbitals appear near the top of the valence band. This result indicates that doping of N atoms into metal oxides is a useful method to develop photocatalysts sensitive to visible light.