金属结合能、线膨胀系数及德拜温度的解析研究与计算

采用两体势模型研究了7类晶系共53种金属的结合能、线膨胀系数及德拜温度,并给出了三者之间普适性的关联方程及解析计算式.理论计算出的线膨胀系数及德拜温度与实验值比较其平均相对误差分别为2.9%和1.66%,相对均方根误差分别为3.75%和2.19%.金属结合能、线膨胀系数及德拜温度三者关联方程中,存在适合于不同晶系结构的共同的关联因子,该因子的均值为1.046,相对均方根误差为2.17%.     

Li2基态结合能的MACQM计算

本文采用改进的排列通道量子力学方法(MACQM),对Li2基态势能曲线进行了计算,结果表明:在核间距R=5.05a0处,能量有极小值-14.88937a.u,由此得到Li2基态结合能为0.0333a.u,所得结果与实验值符合得很好.     

计算金属原子半径和动函数的新方法

提出了一种新的金属准原子模型，以及原子有效价电子数和等价轨道半径等概念。并用该模型和上述概念来研究和处理金属问题。得到：只要已知金属原子核外电子排布规律，给出金属原子的主量子数和价电子总数，就可对所研究的金属原子有效核电荷数、原子半径、金属自由电子密度、费密能和功函数等参量进行有效的定量计算。按照该理论给出的方法和公式，经对６８种金属原子的半径和功函数，以及１７种金属自由电子密度分别进行了计算，并将所得的计算值与相应的实验值进行比较，结果前两者与实验是符合的，后者也比自由电子模型更接近于实际。事实表明，本文提出的模型和方法是符合金属实际的，在应用上可能是有意义的。     

Li9团簇体心立方结构的形成机理和结合能

本文提出了Li9团簇体心立方结构的形成机理,并对此结构的总能量随中心原子到顶点原子间核间距R的变化用芶氏改进的排列通道量子力学方法(MACQM)进行了计算。结果显示曲线在R = 4.77 a0处有一极小值 -67.160922 a.u.,这表明Li9团簇的体心立方结构是可能稳定存在的。在R趋于无穷大时这9个锂原子的总能量为 -66.852240 a.u.,所以形成Li9的总结合能为0.308682 a.u.。因此Li9 团簇的原子平均结合能是0.034298 a.u.或0.933 eV,它大于我们过去计算的Li5团簇正四面体中心结构的原子平均结合能0.632 eV、Li7 团簇正八面体中心结构的原子平均结合能0.674 eV和Li13 团簇正二十面体中心结构的原子平均结合能0.810 eV。故在体心正多面体结构Lin (n= 5 ,7,9,13)中,Li9的体心立方结构有最大的原子平均结合能,这也许是碱金属晶体的晶胞取体心立方结构的一个原因。     

ZA27/CNT界面特性电子理论研究

依据原子结合能定义了界面结合能. 采用递归法计算了纳米管增强锌铝基复合材料中ZA27/CNT界面电子结构，揭示了纳米管在ZA27合金晶界分布的微观物理本质，及其ZA27/CNT弱界面结合的电子层面的原因. 研究发现：金属基体对纳米管增强相上的碳原子态密度影响很大，而纳米管对基体金属中的铝、锌原子影响很小. 碳原子态密度与基体金属原子趋于同化，使纳米管与基体金属结合，但因同化程度不高导致界面结合较弱，影响强化效果. 如果在纳米管装饰或镀上与基体金属性质相近的原子层，会极大改善复合材料的界面结合强度，提高复合材料性能. 关键词： 复合材料 纳米管 电子结构 界面     

SiO2-羟基表面上金属原子的第一性原理研究

采用第一性原理方法研究了SiO₂-羟基表面上几种金属原子的吸附性质，发现In和Ga在SiO₂-羟基表面上的结合很弱，而Fe，Co， Ni在该表面上与Si，O形成强的化学键.等势能面和扩散势垒计算表明In (Ga)的扩散激活能只有0.1—0.3 eV，表明这两种原子容易在表面上扩散.这些结果可以定性地解释纳米合成中的一些实验现象. 关键词： 第一性原理 表面扩散 结合能 金属原子     

FCC金属空位的MAEAM理论研究

应用涉及更远邻原子的改进分析型嵌入原子方法(MAEAM)计算了面心立方(fcc)金属(Ag,Al,Au,Cu,Ir,Ni,Pd,Pt,Rh)的空位性能.在MAEAM计算中,考虑了远邻原子相互作用和单空住迁移能,对两体势进行了坚挺处理,并采用新的截尾函数和加强光滑连接条件对两体势作了截尾处理.同时为了更好的符合面心立方晶体的结合能、弹性常数和平衡条件,调整了多体势的模型常数.未弛豫空住性能计算中考虑了两体势的截尾距离和电子密度分布函数的截尾距离之间近邻原子的作用以及双空位迁移途径周围的原子非对称分布.结果与其它方法计算结果基本一致,但更加接近实验值.对双空住迁移能的计算结果有利地说明了fcc金属双空住5种迁移途径的扩散机制.     

FCC金属结构稳定性和声子谱的MAEAM研究

应用改进分析型嵌入原子方法(MAEAM)计算fcc金属的结构稳定性和声子谱.考虑更远邻原子之间的相互作用,提出新的两体势函数,并采用新的截尾处理函数和加强光滑连接条件.通过拟合单空位迁移能、结合能、三个独立弹性常数及晶体平衡条件,确定了模型参数.在体积不变条件下,计算金属不同结构的能量,说明Ag、Al、Au、Cu、Ir、Ni、Pd、Pt和Rh的fcc结构比较稳定.它们的能量-体积曲线与Rose方程结果基本-致,进-步说明了体积变化时的结构稳定性.同时发现[100]、[110]和[111]三个方向声子谱的计算结果符合实验值和其它计算结果.     

Pu和Au原子4f5/2和4f7/2的结合能计算

基于Koopmans定理,应用MCDF方法计算了Pu和Au原子4f5/2和4f 7/2的结合能以及PuO2所引起的化学位移,一般大于固体的相应值.     

低温下Cu13团簇负载于Cu(001)表面上结构变化的分子动力学研究

应用分子动力学方法研究温度为10和50 K时具有二十面体结构的Cu13团簇以不同接触条件与Cu(001)表面结合后的结构变化,原子间的相互作用势采用Johnson的嵌入原子方法模型.通过基于原子密度分布函数的分析表明,负载团簇与表面的结合能主要受团簇与载体相接触的最低层原子数及这些原子所具有的不同几何构型影响,同时更高层的原子呈现出不同的几何结构.温度为10 K时,负载团簇的初始位置对团簇几何结构和结合能影响较大.     

合金元素韧化或脆化FeAl金属间化合物的微观机制

通过测量二元FeAl以及含B，Zr或Si的FeAl合金的正电子寿命谱参数，计算合金基体和缺陷处的价电子密度.结果表明，当Al原子和Fe原子结合形成FeAl合金时，Al原子提供价电子与Fe原子的3d电子形成局域的共价键.FeAl合金基体的价电子密度很低，FeAl合金中金属键和共价键共存.FeAl合金晶界缺陷的开空间大于Fe空位或Al空位的开空间，FeAl合金晶界处的金属键合力很弱.在FeAl合金中加入少量的B，一部分B原子以间隙方式固溶到FeAl基体中，增加基体的价电子密度；另一部分B原子偏聚到FeAl合金的晶界上，也增加了晶界处的价电子密度.在FeAl合金中加入Zr，增加了合金中的金属键成分，使基体中的价电子密度增加，增强了基体中金属键合力.Zr原子的加入还降低了FeAl合金的有序度，使合金晶界容易弛豫，晶界缺陷的开空间变小.Zr原子在晶界附近出现，还增加了晶界处的价电子密度.在FeAl中加入B或Zr有利于提高合金的韧性.在FeAl合金中加入Si，晶界处的Si原子与邻近的原子形成强的共价键，使得在晶界处参与形成金属键的价电子密度降低.在FeAl中加入Si使合金更脆. 关键词：     

稀土元素的价电子结构和熔点、结合能的关联性

稀土是重要的战略物资资源,有一些已形成产业,在永磁、发光、催化和储氢等方面有着重要的作用. 对稀土及其化合物的研究一直是国内外研究的热点.对稀土原子结构和价电子结构的研究有助于对其的更深刻的理解. 依据固体与分子经验电子理论,对镧系稀土和Sc, Y的价电子结构进行系统地研究, 并以此为基础,对它们的熔点和结合能做进一步分析,分析结果和实验值相符. 研究结果表明:稀土金属的结构与晶格电子和共价电子密切相关,随着晶格电子向共价电子的转换, 稀土金属的熔点趋于增加.稀土的价态变化也是影响电子分布和性能的主因, 如: Sm和Eu的熔点与电子结构的关系不同于其他稀土,外壳层的共价电子之间的转化是其熔点与其他元素之间差别较大的主要原因.稀土的4f电子对结合能的影响大,这是源于其4f电子引发的收缩效应. 此结果揭示了决定稀土熔点和结合能的主要因素是稀土的价电子结构的变化.     

Vapor-liquid (insulator-metal) phase transition in alkali metal vapors

A simple physical model is proposed that describes a vapor-liquid phase transition in alkali metal vapors. The model is based on an assumption made on the character of binding between atoms in the gas phase near the critical point. This is the collective quantum cohesive energy, well-known in the theory of liquid alkali metals, which arises due to the appearance of conduction electrons and is extended to the gas region near the critical point. The parameters of the critical points of the transition and of the binodal are determined on the basis of the model calculation of the binding energy for all alkali metals. Combined, these parameters well agree with experimental results and the predictions made by other authors. The minimum metallic conductivity is evaluated. Its behavior allows one to conclude that vapor-liquid and insulator-metal transitions in alkali metal vapors coincide. This fact sheds light on the Zel’dovich-Landau problem as applied to alkali metal vapors.     

Na||Sb-Pb-Sn液态金属电池电极的价电子结构与热-电性能计算

应用固体与分子经验电子理论系统地研究液态金属池Na||Sb-Pb-Sn电极的价电子结构与热、电性能.研究结果表明:电极合金的价电子结构与其性能密切关联.阴极合金Na_1–xIA_x (IA=K, Rb, Cs)的晶格电子随着掺杂量的增加而减少,诱发合金的熔点、结合能随掺杂量的增加而降低. Na离子输运到阳极,与阳极Sb-Sn-Pb形成产物NaSb_3, NaSn, Na₁₅Sn_4, NaPb.其理论熔点与实验相符. NaSb_3的平均晶格电子数最少,开路电压最高.研究表明:对于Na||Sb-Pb-Sn液态金属电池体系而言,晶格电子扮演重要的角色,可以调控电极的热、电性能.     

On the mechanical stability of bcc transition elements and alloys

A volume independent and a volume dependent lattice energy function involving short-range interatomic potentials were able to be fitted to the elastic constants, cohesive energy, lattice parameter and for the latter function to the vacancy formation energy and bcc-fcc lattice stability energy, as well, for fcc metals and bcc alkali metals, but not to the cohesive energy and C' elastic constant of bcc transition metals. The assumption that directional, but partial, covalent bonds exist between nearest-neighbors in the bcc transition elements provides an explanation for the latter results and in addition explains the identical dependence of C' and the bcc-fcc lattice stability upon N_d, where N_d is the average number of d electrons, for the bcc transition metals and alloys. Both the mechanical and thermodynamic stability of the bcc structure for transition metals and all transition metal alloys disappears for 5 ? N_d > 2 and <?1.     

jj耦合下二价原子精细结构能级的一般表达式

利用表象变换理论以及由拉卡代数方法计算双电子组态ＬＳ谱项能量的结果，导出了ｊ耦合下二价原子精细结构能级的一般表达式     

Cellular approximation of the method of the model electron density functional. Disordered alloys

An expression is obtained, by the method of cells, for the total energy of metals and disordered binary alloys that is accurate up to first order in the deviation of the densities of almost free electrons from their average values. The use of the average values of the electron densities over the Wigner-Seitz cells makes it possible to eliminate the specific form of the interaction potential of almost free electrons with the core and valence d and f electrons and to determine their integral effect in terms of the equilibrium properties of pure metals.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 71–76, May, 1991.     

Electron momentum density and Compton profile by a semi-empirical approach

Here we propose a semi-empirical approach to describe with good accuracy the electron momentum densities and Compton profiles for a wide range of pure crystalline metals. In the present approach, we use an experimental Compton profile to fit an analytical expression for the momentum densities of the valence electrons. This expression is similar to a Fermi–Dirac distribution function with two parameters, one of which coincides with the ground state kinetic energy of the free-electron gas and the other resembles the electron–electron interaction energy. In the proposed scheme conduction electrons are neither completely free nor completely bound to the atomic nucleus. This procedure allows us to include correlation effects.We tested the approach for all metals with Z=3–50 and showed the results for three representative elements: Li, Be and Al from high-resolution experiments.     

Charge transfer and stability of NFE random alloys

The stability of random alloys is determined primarily by a balance between the energy of the volume change upon alloy formation (elastic energy), and the charge transfer between atomic cells. The charge transfer in homovalent, nearly free electron alloys was determined by taking the wave function to be that of the free atoms inside the ion cores, and to be plane waves in the interstitial regions. For a given valence, it was possible to establish an electronegativity series based on charge transfer, to determine charge transfer as a function of composition, and to compute the energy of alloy formation. The theory properly accounts for the formation of alloys of the alkali and alkaline earth metals, and shows why so few such alloys form.     

Correlation between electronic structure and energy band in Eu-doped CuInTe_2 semiconductor compound with chalcopyrite structure

The Eu-doped Cu(In, Eu)Te_2 semiconductors with chalcopyrite structures are promising materials for their applications in the absorption layer for thin-film solar cells due to their wider band-gaps and better optical properties than those of CuInTe_2. In this paper, the Eu-doped CuInTe_2(CuIn_(1-x)Eu_xTe_2, x = 0, 0.1, 0.2, 0.3) are studied systemically based on the empirical electron theory(EET). The studies cover crystal structures, bonding regularities, cohesive energies, energy levels,and valence electron structures. The theoretical values fit the experimental results very well. The physical mechanism of a broadened band-gap induced by Eu doping into CuInTe_2 is the transitions between different hybridization energy levels induced by electron hopping between s and d orbitals and the transformations from the lattice electrons to valence electrons for Cu and In ions. The research results reveal that the photovoltaic effect induces the increase of lattice electrons of In and causes the electric resistivity to decrease. The Eu doping into CuInTe_2 mainly influences the transition between different hybridization energy levels for Cu atoms, which shows that the 3d electron numbers of Cu atoms change before and after Eu doping. In single phase CuIn_(1-x)Eu_xTe_2, the number of valence electrons changes regularly with increasing Eu content,and the calculated band gap E_g also increases, which implies that the optical properties of Eu-doped CuIn_(1-x)Eu_xTe_2 are improved.