Si在TiAl3中取代行为的第一性原理研究

采用基于密度泛函理论的第一性原理方法,研究了Si原子在TiAl3中的格点取代行为.通过对不同原子被置换后的c/a值、形成能以及电子态密度的计算和比较,发现Si原子倾向于取代TiAl3中的Al原子,其取代行为主要由系统的电子结构决定,计算结果与实验相符.为了进一步研究Si原子的取代行为,对Si原子占据的格点以松散或紧凑分布下体系的总能、形成能以及电子态密度进行了计算,结果表明Si原子倾向于取代TiAl3中松散分布的Al(2)原子.对c/a值的计算表明,随Al(2)格点Si原子浓度的增加,c/a值逐渐增大;而当Si取代Al(1)格点时,c/a值随Si原子浓度的增加而减小.研究表明,Si在TiAl3中的极限固溶度介于12.5at%-18.75at%之间.     

Si在TiAl3中取代行为的第一性原理研究

采用基于密度泛函理论的第一性原理方法,研究了Si原子在TiAl₃中的格点取代行为.通过对不同原子被置换后的c/a值、形成能以及电子态密度的计算和比较,发现Si原子倾向于取代TiAl₃中的Al原子,其取代行为主要由系统的电子结构决定,计算结果与实验相符.为了进一步研究Si原子的取代行为,对Si原子占据的格点以松散或紧凑分布下体系的总能、形成能以及电子态密度进行了计算,结果表明Si原子倾向于取代TiAl₃中松散分布的Al（2）原子.对c/a值的计算表明,随Al（2）格点Si原子浓度的增加,c/a值逐渐增大;而当Si取代Al（1）格点时,c/a值随Si原子浓度的增加而减小.研究表明,Si在TiAl₃中的极限固溶度介于12.5at%—18.75at%之间. 关键词： 密度泛函理论 第一性原理 电子结构 3')" href="#">TiAl₃     

Al、N共掺杂实现p-型ZnS的第一性原理研究

 采用基于密度泛函理论的第一性原理平面波超软赝势方法,计算了闪锌矿ZnS、N掺杂以及Al、N共掺杂ZnS晶体的电子结构,分析了N掺杂以及Al和N共掺杂ZnS晶体的能带结构、电子态密度以及Mulliken电荷分布。计算结果表明：N掺杂ZnS在能带中引入了深受主能级,N原子的2p态在价带顶提供了空穴载流子,载流子局域于价带顶附近;Al和N共掺使得受主能级变宽,非局域化特征明显,提高了掺杂浓度和系统的稳定性,更加有利于获得p-型ZnS。     

掺氮四面体非晶碳的第一性原理研究

采用基于第一性原理的分子动力学方法对掺氮四面体非晶碳进行结构建模,并对其显微结构和电子结构进行了研究. 氮在非晶碳网络中的配位形态与密度没有明显关系,主要是以三配位形态存在,其次是两配位,四配位氮的比例很小. 掺氮后碳网络结构sp²含量大大增加,随着氮含量的增加,费米能级附近态密度增加. 氮掺入后并未使费米能级发生明显移动. 关键词： 掺氮四面体非晶碳 第一性原理 密度泛函理论 电子结构     

高压下BeP2N4结构相变和电子结构的第一性原理计算

 基于密度泛函理论的第一性原理方法,计算了硅铍石型和尖晶石型结构BeP₂N₄的总能量随体积的变化关系。利用Brich-Murnaghan状态方程,通过能量和体积拟合,得到了2种结构的体变模量及其对压强的一阶导数。在压力作用下,BeP₂N₄的相变是从硅铍石型结构（空间群R-3,No.148）转变到尖晶石型结构（空间群Fd-3m,No.227）,计算出的相变点与其它理论值符合得非常好。同时计算了BeP₂N₄的相对晶格常数a/a₀和相对体积V/V₀的压缩率,在低压下发现,尖晶石结构BeP₂N₄的压缩率接近金刚石,进一步计算了不同压力下的体弹模量B_H、剪切模量G_H、B_H/G_H和杨氏模量E。此外,对两种结构的BeP₂N₄的电子态密度和带隙随压强的变化关系进行了计算和分析。结果表明：在压力作用下,上价带顶向费米能级移动,并有一定的展宽。Be—N、P—N键缩短,电子转移增加,导致电荷发生重新分布。     

Nb在Ni3Al中取代行为及合金化效应的第一性原理研究

采用基于第一性原理的平面波赝势方法,研究了Nb原子在Ni₃Al中的格点取代行为及合金化效应.通过对不同原子被置换后体系的形成热、结合能及电子态密度的计算和比较,发现Nb原子倾向于取代Ni₃Al中的Al原子,其取代行为主要由系统的电子结构决定,计算结果与实验相符.为了进一步研究Nb原子的取代行为,对Nb原子占据的格点以松散或紧凑分布下体系的总能、形成热、结合能以及电子态密度进行了计算,结果表明Nb原子占据的格点更倾向于紧凑分布.为了研究Nb对Ni_{3关键词： 第一性原理 3}Al合金')" href="#">Ni₃Al合金 电子结构 合金化效应     

加压下ZnO结构相变和电子结构的第一性原理计算

基于密度泛函(DFT)理论的第一性原理,计算半导体ZnO纤锌矿结构和岩盐矿结构状态方程及其在高压下的相变,分析加压下体相ZnO的晶格常数、电子态密度和带隙随压力的变化关系,并将计算结果与文献中的理论和实验数据进行比较.验证在计算金属氧化物时,应用局域密度(LDA)近似计算出的相变压力普遍偏高,采用广义梯度(GGA)近似得到的结果与实验符合较好.     

高压下SiO_2的第一性原理计算

基于密度泛函理论(DFT)的第一性原理,采用Hartree-Fork(HF)方法,分别计算了Si O2的α-石英结构、金红石结构以及氯化钙结构的总能量随体积的变化关系。利用Murnaghan状态方程,通过能量和体积拟合,得到了3种结构的体变模量及其对压强的一阶导数。计算结果表明,随着压强的增加,Si O2会从α-石英结构转变为金红石结构,与实验结果和其它理论结果一致;金红石结构与氯化钙结构之间不存在相变,可以共存。此外,对具有α-石英结构的Si O2的晶格常数、电子态密度和带隙随压强的变化关系进行了计算和分析,结果表明:加压作用下,能带向高能方向移动,Si─O键缩短,电子数转移增加,带隙展宽,电荷发生重新分布。     

ZnO电子结构与光学性质的第一性原理计算

计算了ZnO电子结构和光学线性响应函数,从理论上给出了ZnO材料电子结构与光学性质的关系。所有计算都是基于密度泛函理论框架下的第一性原理平面波超软赝势方法。利用精确计算的能带结构和态密度分析了带间跃迁占主导地位的ZnO材料的介电函数、反射谱、反射率以及消光率,理论结果与实验符合甚佳,为ZnO光电材料的设计与应用提供了理论依据。同时,计算结果也为精确监测和控制ZnO材料的生长过程提供了可能性。     

Ta2O5电子结构和光学性质的第一性原理计算

采用基于密度泛函理论(DFT)框架下广义梯度近似平面波超软赝势方法,计算了Ta2O5的电子结构、态密度和和光学性质。能带结构计算表明,Ta2O5为间接带隙半导体,禁带宽度为2.51eV;价带主要由O 2s和Ta 5d,以及Ta 5d,6s电子态构成,导带主要由Ta 5d和O 2p构成;静态介电常数ε1（0）=3.96;折射率n=2.0。并利用计算的能带结构和态密度分析了Ta2O5的介电常数、吸收系数、折射率、反射率、光电导率和能量损失函数的计算结果,为Ta2O5的设计和应用提供了理论依据。     

钙钛矿型HoNiO_3中电荷歧化的第一原理研究

应用第一原理的密度泛函方法 ,研究钙钛矿型过渡金属氧化物HoNiO3的电子结构 .HoNiO3在正交结构 (空间群为Pbnm)和单斜结构 (空间群为P2 1 n)的电子密度图表明Ni在正交相中只存在Ni3 一种组态 ,而在单斜相中则存在Ni( 3-δ) 和Ni( 3 δ) 两种不同的组态 .电荷歧化特征值δ可由Ni3d电子态密度中非键t2g部分反映 .通过t2g态密度在正交和单斜相的相对变化 ,可以算得δ值为 0 34± 0 0 1.     

First-principles investigation of the electronic structure and magnetism of eskolaite

The electronic structure and magnetism of eskolaite are studied by using first-principles calculations where the on-site Coulomb interaction and the exchange interaction are taken into account and the LSDA+U method is used. The calculated energies of magnetic configurations are very well fitted by the Heisenberg Hamiltonian with interactions in five neighbour shells; interaction with two nearest neighbours is found to be dominant. The Néel temperature is calculated in the spin-3/2 pair-cluster approximation. It is found that the measurements are in good agreement with the calculations of lattice parameters, density of states, band gap, local magnetic moment, and the Néel temperature for the values of U and J that are close to those obtained within the constrained occupation method. The band gap is of the Mott--Hubbard type.     

First-principles investigation of N-Ag co-doping effect on electronic properties in p-type ZnO

The geometric structure, band structure and density of states of pure, Ag-doped, N-doped, and N--Ag codoped wurtzite ZnO have been investigated by the first-principles ultra-soft pseudopotential method based on the density functional theory. The calculated results show that the carrier concentration is increased in the ZnO crystal codoped by N and Ag, and the codoped structure is stable and is more in favour of the formation of p-type ZnO.     

Effect of Cr,Mo, and Nb additions on intergranular cohesion of ferritic stainless steel: First-principles determination

Effects of Cr, Mo, and Nb on the ferritic stainless steel ]2（210） grain boundary and intragranularity are investigated using the first-principles principle. Different positions of solute atoms are considered. Structural stability is lowered by Cr doping and enhanced by Mo and Nb doping. A ranking on the effect of solute atoms enhancing the cohesive strength of the grain boundary, from the strongest to the weakest is Cr, Mo, and Nb. Cr clearly prefers to locate in the intragranular region of Fe rather than in the grain boundary, while Mo and Nb tend to segregate to the grain boundary. Solute Mo and Nb atoms possess a strong driving force for segregation to the grain boundary from the intragranular region, which increases the grain boundary embrittlement. For Mo- and Nb-doped systems, a remarkable quantity of electrons accumulate in the region close to Mo （Nb）. Therefore, the bond strength may increase. With Cr, Mo, and Nb additions, an anti-parallel island is formed around the center of the grain boundary.     

First-principles equations of state for Al,Cu, Mo,and Pb to ultrahigh pressures

Abstract

Using accurate electronic-structure, interatomic-potential, and statistical methods, first-principles theoretical equations of state (EOSs) have been developed for the prototype metals Al, Cu, Mo, and Pb over wide ranges of volume and temperature. Emphasis is given to both the cold compressed solid, relevant to diamond-anvil-cell (DAC) experiments, and to the hot compressed liquid, relevant to multimegabar shock-wave experiments. The A1 EOS has recently been used to analyze nuclear-impedance-match (NIM) shock data on AI-Cu, AI-Mo, and A1-Pb sample pairs in the 5–30 Mbar regime [J. Appl. Phys. 69, 2981 (1991)]. Below 10 Mbar, calculated theoretical Hugoniots are in very good agreement with both absolute and NIM shock data for all four metals. Above 10 Mbar, some quantitative uncertainties remain, especially for Mo. Useful analytic representations of the calculated 300-K isotherms below 10 Mbar have also been developed for fcc Al, Cu, and Pb and for bcc Mo. The theoretical isotherms are in excellent agreement with a variety of ultrasonic, DAC, and reduced-shock data obtained in the assumed phases below 3 Mbar. At higher pressures complicating solid-solid phase transitions are expected and/or observed in Al, Mo, and Pb, but not in Cu, which is consequently a good candidate as a static ultrahigh-pressure EOS standard.     

Adhesion at a heterophase interface: First-principles study of Mo(001)/MoSi2(001)

The bonding characteristics, interfacial energetics, and electronic structure associated with adhesion at the Mo-MoSi₂(001) heterophase interface are investigated using the first-principles, self-consistent local orbital method. We found both the adhesive energy and peak interfacial strength for the interface to be 10%-15% smaller than the respective values for cleavage along the (001) planes in crystalline Mo and MoSi₂. The equilibrium interlayer separation between Mo and MoSi₂ is found to lie between the interplanar spacings of crystalline Mo and MoSi₂. The interfacial adhesive bonding is attributable to the combination of a nearly uniform band of charge accumulation at the interface and directional charge accumulation between atoms across the interface. These first-principles calculations demonstrate that the universal-binding-energy relation can be extended to describe adhesion between dissimilar materials.     

First-principles study of strain effect on the formation and electronic structures of oxygen vacancy in SrFeO_2

Motivated by recent experimental observations of metallic conduction in the quasi-two-dimensional SrFeO_2, we study the epitaxial strain effect on the formation and electronic structures of oxygen vacancy(Vo) by first-principles calculations.The bulk SrFeO_2 is found to have the G-type antiferromagnetic ordering(G-AFM) at zero strain, which agrees with the experiment. Under compressive strain the bulk SrFeO_2 keeps the G-AFM and has the trend of Mott insulator-metal transition.Different from most of the previous similar work about the strain effect on Vo, both the tensile strain and the compressive strain enhance the Vo formation. It is found that the competitions between the band energies and the electrostatic interactions are the dominant mechanisms in determining the Vo formation. We confirm that the Vo in SrFeO_2 would induce the n-type conductivity where the donor levels are occupied by the delocalized d_(x~2-y~2) electrons. It is suggested that the vanishing of n-type conductivity observed by the Hall measurement on the strained films are caused by the shift of donor levels into the conduction band. These results would provide insightful information for the realization of metallic conduction in SrFeO_2.     

CoSi电子结构第一性原理研究

采用基于第一性原理的密度泛函理论全势线性扩展平面波法，首先对CoSi的晶胞参数进行优化计算，CoSi多粒子系统的最低能量为-134684297Ry，此时其晶胞处于最稳态，与最稳态对应的晶胞体积V0等于5899360a.u.3,晶胞参数为a=b=c=04438nm；然后计算了优化后的CoSi的电子结构及Si侧Al掺杂的CoSi075Al025的电子结构并分析了两者的电子结构特征，计算的CoSi电子能态密度与已有的计算结果整体形貌相同，但存在局部差异，Al掺杂后费米面发生了偏移；最后探讨了两者的电子结构对热电性能的影响，Al掺杂可提高CoSi的材料参数B，因此有望提高其热电性能. 关键词： 第一性原理 电子结构 热电性能     

Ta掺杂对ZnO光电材料性能影响的研究

采用基于密度泛函理论第一性原理的方法, 研究了Ta掺杂ZnO的电子结构和光学性质. 计算结果表明: 掺入Ta原子后, 费米能级进入导带, 随着掺杂浓度的增加, 带隙逐渐变窄, 介电函数虚部、吸收系数、反射率和折射率均发生明显变化, 介电函数虚部和反射率均向高能方向移动, 吸收边发生红移, 从理论上指出了光学性质和电子结构的内在联系.