Y(Fe,M)12化合物的电子结构与磁性(M=Nb,Si)

采用新近发展的全势能线性缀加平面波((L)APW) 局域轨道(lo)和广义梯度近似(GGA)密度泛函方法计算了Y(Fe,M)12化合物(M=Nb,Si)的电子结构,得到了相应的总态密度和局域态密度,并分析了替代原子与替代晶位不同引起态密度的变化。根据计算结果预测的居里温度变化与实验结果基本一致。     

CdTe(111)表面的稳定性研究

利用Muffin-Tin轨道线性组合法(LMTO),采用Slab模型,不仅计算了CdTe(111)表面两类模型四种表面的电子结构,给出了总态密度,包括表面态在内的局域及分波态密度,而且与同步辐射实验结果比较分析了这些模型表面结构的稳定性;阐明了清洁理想CdTe(111)表面存在时,表层原子可能存在状态,该结果与Wu等的实验结果符合。 关键词：     

Au钝化Si(100)表面的电子特性

用TB-LMTO方法研究单层的Au原子在理想的Si(100)表面的化学吸附.计算了Au原子在不同位置的吸附能,吸附体系与清洁Si(100)表面的层投影态密度, 以及电子转移情况.结果表明, Au原子在吸附面上方的A位(顶位)吸附最稳定, Au钝化Si(100)表面可以取得明显的钝化效果, 这一结论与实验事实相符合.     

S钝化GaAs(100)表面的电子特性

用TB-LMTO方法研究单层的S原子在理想的GaAs (100) 表面的化学吸附, 对GaAs(100)表面是Ga-和As-中断两种情况分别进行考虑. 计算了S原子在不同位置的吸附能、吸附体系与清洁的GaAs(100)表面的层投影态密度, 以及电子转移情况. 结果表明, 两种情况下S原子都是桥位吸附最稳定, S-Ga相互作用比S-As稍强, S钝化GaAs(100)表面可以取得明显的钝化效果.     

FeS2(100)表面原子几何与电子结构的理论研究

采用密度泛函理论研究了FeS2(100)表面原子几何与电子结构.理论计算结果表明:FeS2(100)表面无弛豫、无重构,是体相原子几何的自然终止.与体相电子结构相比,FeS2(100)表面电子特性明显不同,禁带中央产生新的表面态,且表面态局域性强,主要由Fe原子的3d分波贡献.配位场理论定性分析表明:FeS2(100)完整晶面表面态产生机制是Fe原子的配位数减少、局部对称性下降所致 关键词： 密度泛函理论 表面电子结构 FeS2     

Mn掺杂的ZnS(001)表面的电子态特性

利用第一性原理计算Mn在ZnS(001)表面上几种掺杂位置的形成能、局域分波态密度和磁矩.对Mn在ZnS(001)表面上的三种位置的形成能进行比较,得到两种填隙位置是非常稳定的掺杂位置.分析ZnS(001):Mn各种再构表面的电子态密度和电荷密度分布.结果表明,三种表面模型中,自旋向上的Mn原子的3d态和近邻S原子的3p态都有一定的杂化,并且替代掺杂的Mn和邻近S原子的p-d杂化最明显,形成的共价键最强.而自旋向下的Mn原子的3d态比较局域,受S原子的3p态影响较小.计算了三种掺杂表面的磁矩,并分析计算结果.     

不同密度氢吸附金刚石(100)表面的微观结构

利用基于广义梯度近似的密度泛函理论,计算了金刚石(100)表面不同氢吸附密度的平衡态几何结构和态密度.结果表明对于2×1构型,在平行和垂直表面两个方向上发生弛豫,而1×1构型仅在垂直表面方向上发生弛豫.另外,清洁2×1,2×1 ∶0.5H和1×1 ∶1.5H表面,带隙中存在空表面态;而对于1×1 ∶2H和2×1 ∶H两种表面结构,空表面态上移进入导带,带隙中不存在表面态.结合电荷密度分布,探讨了金刚石(100)不同构型和氢吸附密度表面的表面态诱发机理. 关键词： 氢吸附 金刚石 弛豫 表面态     

碳吸附于Fe（100）表面的第一性原理研究

本文采用自旋极化密度泛函理论计算了清洁Fe（100）表面及C吸附于Fe（100）表面三种结构: p(2×2)、c(2×2)及p(2×1)。清洁Fe(001)表面只有弛豫,没有重构。吸附C原子的Fe表面体系,最稳定位置为四重空位,空位吸附的C原子实际上与Fe成五重键,这与实验相符。通过对c(2×2)表面结构的电子态密度计算,发现C原子的s、p态与表面Fe原子的d、p及s态都有不同程度的相互作用,成键的主要作用为C2p态与Fe3dx2-y2、3dxy 态的杂化。     

硫在Fe(100)面吸附的第一性原理研究

基于密度泛函理论的第一性原理方法,在广义梯度近似下,计算了硫原子在Fe(100)面吸附的结构和电子性质,并计算了其分子轨道和吸附能.同时讨论了相关吸附性质与硫原子表面覆盖度(0.25～1.0ML)的关系.结果表明:硫原子吸附在H住最稳定,吸附能均随浓度的增加而单调增加;B位吸附的硫原子与Fe(100)表面的距离随浓度非单调变化,在0.5 ML时达到最大,是由较高的局域电子云重叠产生的排斥作用所导致;对比分析吸附前后硫和Fe的s及p电子的态密度,显示了硫化亚铁的生成.     

硫在Fe(100)面吸附的第一性原理研究

基于密度泛函理论的第一性原理方法,在广义梯度近似下,计算了硫原子在Fe(100)面吸附的结构和电子性质,并计算了其分子轨道和吸附能.同时讨论了相关吸附性质与硫原子表面覆盖度(0.25-1.0ML)的关系.结果表明：硫原子吸附在H位最稳定,吸附能均随浓度的增加而单调增加;B位吸附的硫原子与Fe(100)表面的距离随浓度非单调变化,在0.5ML时达到最大,是由较高的局域电子云重叠产生的排斥作用所导致的;对比分析吸附前后硫和Fe的s及p电子的态密度,显示了硫化亚铁的生成.     

Anomalous density of states in hybrid normal metal-superconductor bilayers

In contact with a superconductor, the Andreev reflection of the electrons locally modifies the N metal electronic properties, including the local density of states (LDOS). We investigated the LDOS in superconductor-normal metal (Nb-Au) bilayers using a very low temperature (60 mK) STM on the normal metal side. High resolution tunneling spectra measured on the Au surface show a clear proximity effect with an energy gap of reduced amplitude compared to the bulk Nb gap. The dependence of this mini-gap width with the normal metal thickness is discussed in terms of the Thouless energy. Within the mini-gap, the density of states does not reach zero and shows clear sub-gap features. We compare the experimental spectra with the well-established quasi-classical theory.     

Electronic properties of TiC(100) and polar TiC(111) surfaces

The energy bands of films of TiC have been calculated using the linear-combination-of-atomic-orbitals method with parameters obtained by a fit to the bulk band structure. The Madelung potentials and charge redistribution have been determined self-consistently. For the neutral TiC(100) surface, the density of states (DOS) is similar to that of the bulk. For the non-neutral Ti-covered TiC(111) surface, Ti 3d-derived surface states appear around the Fermi energy E_F. The long-range electric field produced by the polar surfaces is screened by the charge redistribution, and the polar surfaces are stabilized. Characteristic features of TiC(111) compared to other surfaces of TiC are attributed to the high surface DOS at E_F.     

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     

原子围栏中金属表面电子的态函数及能级

本文用薛定谔方程求解被束缚在原子围栏中金属表面电子的态函数及能级,同时用计算机绘制出围栏中电子概率分布图。     

铌合金电子结构及其高温氧化行为

为了从电子层面揭示Nb合金高温氧化的物理本质,采用递归法计算了Nb合金的电子态密度、原子镶嵌能、亲和能等电子结构参数,探索Nb合金高温氧化机理.研究表明:氧在Nb中具备较高的扩散速率和溶解度,且氧与Nb较易发生反应,生成氧化物,这使Nb的抗高温氧化性较差.原子镶嵌能的计算结果表明,合金元素Ti,Si,Cr在基体中稳定性较低,易向Nb合金表面扩散,形成富Ti,Si,Cr的表层.合金表层中氧与Nb,Ti,Si,Cr间具有较大亲和性,可以生成相应的氧化物,形成对合金具有保护作用的氧化膜. 关键词： 递归法 高温氧化 Nb合金     

First-principles investigations of ordering in binary α-Ti solid solutions

The ordering tendency in binary f-Ti solid solution containing 3sp or 4sp simple-metal (SM) or 3d transition-metal (TM) solute is investigated systematically by the linear muffin-tin orbital (LMTO) method within the atomic sphere approximation (ASA). We demonstrated that the effective pairwise interaction (EPI) energy in a solid solution is equal to half the solute-solute interaction energies and can be evaluated by a supercell total energy approach. The calculations of EPI energy both with and without volume relaxation of the supercells and local density of states (LDOS) show that the EPI energies of Ti-SM and Ti-TM solutions are dominated by different factors. For Ti-SM solutions, the EPI energies are of large absolute values with a negative sign, indicating strong ordering tendency in these solutions. The volume relaxation does not alter the EPI energy substantially. The calculated LDOS shows that the ordering tendency in Ti-SM solutions may be related to the hybridization between the electrons of the SM atoms when they are close to each other. For most Ti-TM solutions, if calculated without relaxation, the absolute EPI energies are very small; however, if calculated with relaxation, they are of relatively large positive values, indicating a clustering tendency in these solutions. By combining the calculated EPI energy and Flinn's model for short-range order (SRO) strengthening, the increase in critical shear stress sro due to SRO is estimated for Ti-SM alloys, and the results qualitatively agree with experiment.     

Self-consistent electronic structure for a Mo (001) surface with saturated H adsorption

The band structure for a Mo (001) surface covered with a saturated monolayer of hydrogen is calculated self-consistently using the pseudopotential method in a mixed-basis representation. Two adsorbate bands are found below the bottom of the molybdenum bulk bands. Most of the intrinsic surface states of the clean (001) surface also exist on the hydrogen covered surface at lower energies. The results are used to identify H induced structures observed in recent photoemission studies of hydrogen on W (001).     

Density of states of superlattices with multiple layers per period

Density-of-states (DOS) investigations of polytype superlattices (SLs), whose period consists of more than two different layers, are presented. Local DOS (LDOS) is computed as a function of both the electron energy and the space coordinate, which illustrates — in a direct way — the spatial localization, over the SL period, of states forming the energy minibands. A few examples of AlGaAs-based polytype SLs with a coupled-well, step-well and δ-doped basis are analysed, indicating that various LDOS distributions within SL minibands can be arranged. By changing the basis geometry, the electronic DOS can either be selectively confined to a particular SL layer or extend over the whole SL period, which provides a means of modifying the spatial overlap of states from different SL minibands and thus, tuning the respective interband transitions. In particular, polytype SLs with similar miniband structures may exhibit essentially different LDOS features and, consequently, the different transport and optical characteristics. Therefore, it is emphasized that — for a particular device application of a complex-basis SL — not only the electronic level structure should be appropriately designed, but also the corresponding space-charge distributions should be carefully considered.     

Nb掺杂γ-TiAl金属间化合物的电子结构与力学性能

运用基于密度泛函理论的第一性原理方法计算了Nb掺杂γ-TiAl金属间化合物的结构参数、能带结构、电子态密度及弹性常数.结果表明:Nb替代Ti掺杂相比Nb替代Al掺杂的形成能低,Nb在替位掺杂时更倾向于取代Ti原子形成稳定的结构,Nb替代Ti掺杂能够提高γ-TiAl金属间化合物的抵御塑性变形能力、断裂强度和延展性;与Nb替代Ti掺杂相比,Nb替代Al掺杂同样增强γ-TiAl金属间化合物的断裂强度且其增强延展性的效果更好,但抵御塑性变形的能力有所削弱.     

First-principles study of electronic properties of interfacial atoms in metal-metal contact electrification

The mechanism of contact electrification between metals was studied using the first-principles method, taking the Ag-Fe contact as an example. Charge population, charge density difference, the orbitals and densities of states (DOS) were calculated to study the electronic properties of the contacting interfacial atoms. Based on the calculation, the amount of contact charge was obtained. The investigation revealed that the electrons near Fermi levels with higher energies transfer between the outermost orbitals (s orbitals for Ag and d orbitals for Fe). Meanwhile, polarized covalent bonds form between the d electrons in the deep energy states. These two effects together lead to an increase of charge magnitude at the interface. Also, the electrons responsible for electrification can be determined by their energies and orbitals.