Ni,Al及其合金的一种嵌入原子势

嵌入原子势在金属材料的结构及其物性的计算机模拟方面仍然有着重要的作用.针对面心立方结构的镍、铝及其合金,我们拟合了一种简单形式的嵌入原子势.势参数的拟合使用了相应材料的晶格常数,结合能、空位形成能以及三个弹性常数C_(11),C_(12),C_(44).除了一些高频部分的合理偏差之外,使用拟合的势参数得到的声子谱与实验结果符合良好.此外,得到的状态方程也与第一原理的理论结果很好地符合,说明了此嵌入原子势的可靠性.     

金红石结构TiO2晶体点缺陷形成能的经验途径计算

基于经验参数化途径 ,通过对晶体结构、晶格形成能、介电性质和弹性实验数据拟合确定金红石结构氧化物晶体TiO2 的电子壳模型参数和非Coulomb互作用势参数 .计算点缺陷形成能 .论证Schottky缺陷是金红石结构TiO2中的本征缺陷 .     

金红石结构TiO2晶体点缺陷形成能的经验途径计算

基于经验参数化途径,通过对晶体结构、晶格形成能、介电性质和弹性实验数据拟合确定金红石结构氧化物晶体TiO₂的电子壳模型参数和非Coulomb互作用势参数.计算点 缺陷形成能.论证Schottky缺陷是金红石结构TiO₂中的本征缺陷. 关键词： 2')" href="#">金红石TiO₂ 点缺陷形成能 电子壳模型 经验途径计算     

金属Nb的Finnis-Sinclair势开发及势函数形式对材料性能的影响

对于计算材料科学的研究者来说,经常由于找不到合适的原子间势而工作受阻.本文将在Finnis-Sinclair势的框架下,通过开发金属Nb的Finnis-Sinclair势而给出较详细的原子间势拟合、检验、修正的过程.首先建立原子间势与材料宏观性能之间的关系,然后通过再现金属Nb的结合能、体模量、表面能、空位形成能及平衡点阵常数的实验数据的方法拟合金属Nb的Finnis-Sinclair势.利用所构建的原子间势计算金属Nb的弹性常数、剪切模量及柯西压力来检验势函数.讨论势函数曲线形状对间隙形成能的影响,进而根据间隙能的计算数据修正已构建的原子间势.讨论截断距离的处理方法.本文的结果一方面为构建原子间势函数库提供资料,为构建与Nb相关的合金原子间势奠定基础;另一方面,为开发和改善原子间势质量提供方法和依据.     

铝的嵌入原子模型参数和性能计算

运用普适的嵌入原子理论 (GEAM)计算了FCC结构金属铝的嵌入原子模型参数 ,并用该模型计算了铝的单空位形成能、双空位结合能、表面能、结构稳定性、弹性常数和声子谱等性质。计算结果与已有的实验结果相符     

Zn-Mg合金的长程Finnis-Sinclair势

通过拟合Mg的晶格能、晶格常数、弹性常数,并将其与前人的结果相比较后获得了描述Mg的最优长程Finnis-Sinclair(F-S)势函数参数,使用同样方法并引入修正因子后得到了Zn的长程F-S势参数.基于单质Zn,Mg的F-S势参数,进一步拟合合金Mg₂₁Zn₂₅,MgZn₂,Mg₂Zn₁₁的晶格常数、晶格能获得Zn-Mg原子对的F-S势参数,构建了整套描述Zn-Mg合金的长程F-S势参数.在此 关键词： 长程Finnis-Sinclair势 Zn-Mg合金 分子动力学模拟     

高压下TiC的弹性、电子结构及热力学性质的第一性原理计算

利用基于密度泛函理论的第一性原理平面波赝势方法 并结合准谐徳拜模型研究了NaCl结构的TiC在高压下的弹性性质、电子结构和热力学性质. 计算所得零温零压下的晶格常数、体弹模量及弹性常数与实验值符合得很好. 零温下弹性常数和弹性模量随压强增大而增大. 通过态密度和电荷密度的分析, Ti-C键随压强增大而增强. 运用准谐德拜模型, 成功计算了TiC在高温高压下的体弹模量、熵、热膨胀系数、徳拜温度、 Grüneisen参数和比热容. 结果表明压强对体弹模量、热膨胀系数和徳拜温度的影响大于温度对其的影响. 热容随着压强升高而减小, 在高温高压下, 热容接近Dulong-Petit极限.     

高压下硫化钙的弹性和热力学性质的第一性原理计算

利用基于密度泛函理论的第一性原理平面波赝势方法结合准谐德拜模型研究Na Cl结构的Ca S在高压下的弹性和热力学性质.计算得到的零温零压下的晶格常数、体弹模量与实验值符合得很好.弹性常数和弹性模量随着压强的增大而增大.压强对体弹模量和热膨胀系数的影响大于温度的影响.热容随压强的升高而降低,在高温下热容接近于Dulong-Petit极限.通过求解Gibbs自由能计算得到B1结构和B2结构Ca S的相变压为36.61 GPa.     

铀的弹性、能带结构和光学常数的第一性原理计算

采用密度泛函理论,赝势平面波方法计算了金属铀a相的晶体结构,弹性常数,体模量,电子能带结构和光学常数(折射率n和消光系数k)等.其中,铀的晶格参数,弹性常数和体模量等与实验及其它第一性原理计算结果十分吻合.计算得到了铀的光学常数,与实验结果作了对比并进行了分析说明.     

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位迁移能,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。未弛豫空位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。对双空位迁移能的计算结果有利地说明了fcc金属双空位5种迁移途径的扩散机制。     

A new many-body potential with the second-moment approximation of tight-binding scheme for Hafnium

In this work,we develop a new many-body potential for alpha-hafnium(α-Hf)based on the second moment approximation of tight-binding(TB-SMA)theory by introducing an additional Heaviside step function into the potential model and a new analytical scheme of density function.All the parameters of the new potential have been systematically evaluated by fitting to ground-state properties including cohesive energy,lattice constants,elastic constants,vacancy formation energy,structure stability and equation of state.By using the present model,the melting point,melt heat,thermal expansion coefficient,point defects,and low-index surface energies ofα-Hf were calculated through molecular dynamics simulations.Comparing with experiment observations from others,it is shown that these properties can be reproduced reasonably by the present model,some results being more consistent to the experimental data than those by previous suggested models.This indicates that this work is sutiable in TB-SMA potential for hexagonal close packed metals.     

Phenomenological interatomic potentials for silicon, germanium and their binary alloy

A phenomenological potential is constructed for silicon, germanium, and their binary alloy. As in the modified embedded atom model (MEAM), the interatomic interactions are assumed to arise from the overlap of the electron wave functions. However, the calculation of energy is quite different in the two models. The proposed potential has seven adjustable parameters in contrast to ten or more in MEAM but gives perfect fit with the measured values of seven most important quantities for characterizing strained silicon: cohesive energy, equilibrium lattice constant, vacancy formation energy, Raman frequency, and the three elastic constants. The potential should be suitable for lattice statics calculations on strained silicon.     

L12型铝合金的结构、弹性和电子性质的第一性原理研究

运用第一性原理方法研究了L12型铝合金相Al3Sc和Al3Zr的晶体结构、电子结构和弹性.结合能和形成能的计算表明,两种合金具有较强的合金化能力,且Al3Zr较Al3Sc具有更强的结构稳定性.电子结构分析表明,费米能级以下较多的价电子数决定了Al3Zr具有较强的结构稳定性.计算并分析比较了两种合金相的单晶弹性常数(C11,C12和C44)以及多晶弹性模量(体弹性模量B、剪切模量G、杨氏模量Y、泊松比ν和各向异性因子A).通过对比实验和其他理论计算结果,进一步分析和解释了两种合金相的力学性质.     

Theoretical calculations of structural,electronic, and elastic properties of CdSe_(1-x)Te_x:A first principles study

The plane wave pseudo-potential method was used to investigate the structural, electronic, and elastic properties of Cd Se_(1-x)Te_x in the zinc blende phase. It is observed that the electronic properties are improved considerably by using LDA + U as compared to the LDA approach. The calculated lattice constants and bulk moduli are also comparable to the experimental results. The cohesive energies for pure Cd Se and Cd Te binary and their mixed alloys are calculated. The second-order elastic constants are also calculated by the Lagrangian theory of elasticity. The elastic properties show that the studied material has a ductile nature.     

Chen’s lattice inversion embedded-atom method for Ni-Al alloy

The structural properties,the enthalpies of formation,and the mechanical properties of some Ni-Al intermetallic compounds(NiAl,Ni3Al,NiAl3,Ni5Al3,Ni3Al4) are studied by using Chen’s lattice inversion embedded-atom method(CLI-EAM).Our calculated lattice parameters and cohesive energies of Ni-Al compounds are consistent with the experimental and the other EAM results.The results of enthalpy of formation indicate a strong chemical interaction between Ni and Al in the intermetallic compounds.Through analyzing the alloy elastic constants,we find that all the Ni-Al intermetallic compounds discussed are mechanically stable.The bulk moduli of the compounds increase with the increasing Ni concentration.Our results also suggest that NiAl,Ni3Al,NiAl3,and Ni5Al3 are ductile materials with lower ratios of shear modulus to bulk modulus;while Ni3Al4 is brittle with a higher ratio.     

Thermodynamical properties and defect energetics of an n-body potential adapted to Cu3Au

By using molecular statics, molecular dynamics, and Monte Carlo techniques we validate a previously developed empirical n-body potential adapted to Cu₃Au. At T=0 K, predicted cohesive energies, lattice parameters, and elastic constants in CuAu and CuAu₃ as well as the formation energy of vacancies in Cu₃Au are in good agreement with experimental data. A satisfactory behavior is also obtained at T 0 K in Cu₃Au, for atomic mean-square displacements and elastic moduli. However, this model underestimates the vacancy migration energy and the order-disorder critical temperature when the latter is evaluated by Monte Carlo including both exchanges between atoms of different species and atomic moves simulating vibrations.     

嵌入原子法研究Ni3Al中点缺陷以及Re择优占位和集团化

基于纯金属元素Ni，Al和Re的基本物理性质，建立了一个Ni-Al-Re三元体系的分析型嵌入原子多体势.结合分子动力学计算了Ni₃Al的平衡晶格常数、弹性模量、结合能、空位形成能以及反位置缺陷形成能，并分析了Ni₃Al中点缺陷的存在形式.计算结果表明，当成分偏离理想化学配比时出现反位置缺陷.同时研究了Re在Ni₃Al中的择优占位以及Re在Ni₃Al和Ni中的集团化行为.计算结果表明，Re在Ni₃Al中优先置换Al的位置，且发现当Re原子团的尺寸接近于11?时，Re原子团的长大趋势变弱.计算结果与实验以及其他的理论计算结果相符合. 关键词： 嵌入原子势 3Al')" href="#">Ni₃Al Re 占位 集团化