共查询到19条相似文献,搜索用时 437 毫秒
1.
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. 相似文献
2.
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. 相似文献
3.
本文利用分子动力学方法研究了KCl晶体在ρ=ρ0时的温度相变。面心立方(fcc)和体心立方(bcc)两种结构的径向分布函数随温度的变化的情况说明,在高压下,发生着bcc结构相fcc结构的转变,bcc结构是不稳定的。为了选取合理的势参数,利用了分子动力学程序在T=0时的性质,计算了NaCl和KCl晶体的零温状态方程,研究了它们在压力作用下发生的多形性相变。计算表明,NaCl和KCl晶体将分别于18.8 GPa和5.9 GPa发生从fcc到bcc的多形性相变,这些值相当接近实验结果。着说明本文选用的势参数势有一定精度的。 相似文献
4.
5.
6.
7.
为了构建拟合势需要的数据库,采用密度泛函理论方法计算了六角密堆结构钇(hcp-Y)的晶格参数、弹性常数、内聚能、结构能差以及相关的点、面缺陷性质. 基于解析型键序作用势,构建了hcp-Y的多体作用势模型. hcp-Y势模型是通过拟合Y的晶格参数、弹性常数、体弹模量、内聚能、空位形成能和不同相之间的结构能差而构建.分析发现,所得到的势模型能够很好地描述hcp-Y的自填隙原子形成能、空位形成能、双空位键能以及其它体性质,同时,构建的势模型用来研究Y的热动力学性质的相关结果也比较理想. 相似文献
8.
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. 相似文献
9.
10.
采用Quantum Sutton-Chen(Q-SC)多体势对液态金属Cu在四个不同冷却速率下的凝固过程进行了分子动力学模拟研究. 通过双体分布函数、键型指数、配位数、均方位移及可视化分析, 结果表明:冷却速率对液态金属Cu的微观结构演变有决定性影响. 当冷却速率为1.0×1014K/s时得到非晶态结构;当冷速分别为1.0×1013K/s,1.0×1012K/s和1.3×1011K/s时,系统形成以1421键型为主体的面心立方(fcc)与六角密集(hcp)共存的混合晶体结构;且其结晶温度分别为373K,773K和873K,即冷速越慢,其结晶温度越高,结晶程度也越高;且冷速越慢,1421键型越多,混合晶体中面心立方(fcc)结构所占的比例越高. 同时发现,原子的平均配位数的变化与1551,1441,1661键型的变化密切相关, 反映出体系对称性结构的变化规律与配位数的变化有关. 在可视化分析中,进一步采用中心原子法展现出非晶态与晶体结构的2D截面,及在3D下混合晶体中两个基本原子团分别为面心立方(fcc)与六角密集(hcp)基本原子团的具体结构.
关键词:
Q-SC多体势
液态金属Cu
凝固过程
分子动力学模拟 相似文献
11.
The modified analytic embedded atom model (EAM) potentials considering farther neighbor atoms are improved for the noble metals (Ag, Au, Pt, Pd, Rh) and Cu. We not only adopt an end processing function and an enhanced smooth continuous condition for the pair potential, but also adjust the model parameters of multi-body potential by fitting a cohesive energy, a mono-vacancy formation energy, the Rose equation curve for the cohesive energy as a function of lattice parameter, a structure energy difference, elastic parameters and an equilibrium condition of crystal. The calculation results of structure energy differences misfit the experiment data for the noble metals and Cu in the unimproved EAM, because anyone of these differences have not been considered in the calculation of its model parameters. After the modification, the model showed better simulation results for the noble metals and Cu. 相似文献
12.
Tsuyoshi Maeda 《Journal of Physics and Chemistry of Solids》2005,66(11):1924-1927
In order to quantitatively evaluate the formation energies of Cu, In/Ga/Al and Se vacancies in chalcopyrite-type CuInSe2 (CIS), CuGaSe2 (CGS) and CuAlSe2 (CAS), first-principles pseudopotential calculations using plane-wave basis functions were performed. All calculations were performed using a supercell with 64 atoms, which was eight times greater than the number of atoms in a primitive cell with eight atoms. The formation energies of point defects were calculated as a function of the atomic chemical potentials of constituent elements. Atomic arrangements around the vacancy were optimized allowing relaxation of the first- and second-nearest-neighbor atoms of the vacancy. The obtained results were as follows: (1) the formation energy of Cu vacancy was smaller than those of the other vacancies in CIS, CGS and CAS. Under the Cu-poor condition, the formation energy of Cu vacancy in CIS was lowest among those in them; (2) the formation energy of Se vacancy in CIS was relatively lower than those in CGS and CAS; (3) the formation energy of (2VCu+InCu) pair in CIS was greatly dependent on the chemical potential of the constituent elements, i.e. Cu, In and Se. On the other hand, the formation energies of (2VCu+GaCu) in CGS and (2VCu+AlCu) in CAS were not largely dependent on the chemical potential of the constituent elements. Under the Cu-poor condition, the formation energy of (2VCu+InCu) pair in CIS was much lower than those of (2VCu+GaCu) in CGS and (2VCu+AlCu) in CAS. 相似文献
13.
基于密度泛函理论的第一性原理计算, 研究了含B原子空位(VB), N原子空位(VN), 以及含B–N键空位 (VB+N)缺陷的二维氮化硼(h-BN)的电子和磁性质. 在微观结构上, VB体系表现为在空位附近的N原子重构成等腰三角形, VN体系靠近空穴的B 原子形成等边三角形, VB+N体系靠近空穴处的B和N原子在h-BN平面上重构为梯形. 三种空位缺陷都使h-BN的带隙类型从直接带隙转变为间接带隙. VB体系的总磁矩为1.0 μB, 磁矩全部由N原子贡献. 其中空穴周围的三个N原子磁矩方向不完全一致, 存在着铁磁性和反铁磁性两种耦合方式. 对于VN 体系, 整个晶胞内的总磁矩也为1.0 μB, 磁矩在空穴周围区域呈现一定的分布.
关键词:
二维h-BN
空位
电子结构
磁性 相似文献
14.
A scheme for construction of the pair potential from non-empirical calculations of electronic structure of solids is suggested. As an example, parameters of Lennard-Jones potential are obtained for fcc Cs, based on LMTO calculations of energy parameters. Vacancy formation and migration energies for fcc Cs are calculated from this first-principles pair potential. In addition, the frequency of vibration and the jump probability of an atom are calculated and it is shown that they are direction dependent. 相似文献
15.
本文采用基于密度泛函理论的第一性原理赝势法,分析了ZnO:Mn掺杂体系中本征空位缺陷V_(Zn)和V_O分别出现在相对Mn为近邻、次近邻、远次近邻位置时体系的晶体结构、能带分布、态密度和磁性.结果表明:ZnO:Mn体系中V_(Zn)比V_O更容易产生,且两种缺陷均更容易在Mn的近邻位置形成.其中V_(Zn)的出现没有明显改变ZnO:Mn体系的带隙,然而会使体系的导电性增加,且V_(Zn)与Mn的距离越远,导电性越强.同时,V_(Zn)减弱了体系的磁性,但与V_(Zn)的位置无关. V_O的出现会使体系带隙变宽,且电导率显著低于无缺陷ZnO:Mn体系,但是其导电性会随着V_O与Mn的距离变远而增强.同时,V_O的出现不会影响体系原来的磁性. 相似文献
16.
采用基于密度泛函理论的第一性原理,研究了稀土La对bcc-Fe中Cu析出行为的影响.计算了α-Fe中La原子和Cu原子与空位之间,以及La原子和Cu原子之间的点缺陷结合能;在此基础上,讨论了α-Fe中La对Cu扩散激活能的关系.结果表明:La原子与空位之间有较强的相互吸引作用,且对近邻Cu原子也有一定的束缚.此外,La的加入使Cu原子近邻的空位形成能显著升高,这表明La,Cu偏聚区形成空位较为困难.与此同时,由于La原子对近邻空位和Cu原子的吸引作用,使Cu原子向近邻空位跳跃的迁移能有所升高.迁移能与空位形成能变化的计算结果显示,La原子的加入能够使α-Fe中Cu的扩散激活能显著升高,从而延缓了铁素体区富铜相的偏聚和析出. 相似文献
17.
X. Q. Dai J. H. Zhao M. H. Xie Y. N. Tang Y. H. Li B. Zhao 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,80(3):343-349
Spin-polarized density functional theory has been used to study the effects of vacancy defects on the magnetic properties
of graphene. Structural optimization shows that introducing a carbon vacancy cluster into a graphene sheet changes the spatial
distribution of the neighbor atoms, particularly those located around the vacancy. From spin-polarized DOS and LPDOS calculations,
we find that only vacancies containing unpaired electrons show magnetism. These results lead us to formulate a relation between
the vacancy-induced magnetic moment and the size and shape of the vacancy clusters in graphene sheet. 相似文献
18.
Construction of embedded-atom-method interatomic potentials for alkaline metals (Li,Na,and K) by lattice inversion
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The lattice-inversion embedded-atom-method interatomic potential developed previously by us is extended to alkaline metals including Li,Na,and K.It is found that considering interatomic interactions between neighboring atoms of an appropriate distance is a matter of great significance in constructing accurate embedded-atom-method interatomic potentials,especially for the prediction of surface energy.The lattice-inversion embedded-atom-method interatomic potentials for Li,Na,and K are successfully constructed by taking the fourth-neighbor atoms into consideration.These angular-independent potentials markedly promote the accuracy of predicted surface energies,which agree well with experimental results.In addition,the predicted structural stability,elastic constants,formation and migration energies of vacancy,and activation energy of vacancy diffusion are in good agreement with available experimental data and first-principles calculations,and the equilibrium condition is satisfied. 相似文献
19.
N. V. Krainyukova 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):45-48
The energetics of large multiply twined particles (MTPs)
such as decahedra with fivefold symmetry, face-centred cubic (fcc) and
hexagonal close-packed (hcp) clusters in size from 2000 to ~45000 atoms was numerically analysed. Clusters were relaxed freely
under the
Lennard-Jones pair potential to the energy minimum. The essential extension
of size compared to previous studies and the additional shape-optimisation
of hcp and fcc clusters as well as truncated decahedra appears to be of high
importance in the potential energy analysis. The best-optimised decahedra
were confirmed to be the most favourable structure from 2000 to ~105 atoms. Only in the short size interval, above N ∼10000 atoms,
the best-optimised fcc clusters and simplest Marks' decahedra could
alternate, while above N ∼14000 atoms does the shape-optimised hcp
structure be proved to become more favourable for single crystal particles
compared to the best-optimised fcc structure. Depending on shapes and sizes,
decahedra and hcp clusters can alternate in the wide size interval above N ∼
14000 atoms and presumably form the mixed abundances of clusters belonging
to the both symmetries. Finally, the upper limit for stable MTPs was
estimated to be about N ∼105 atoms, while above only the hcp
clusters are the most favourable. 相似文献