共查询到20条相似文献,搜索用时 234 毫秒
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用局域密度总能方法研究了两种不同(DO22和L12)相结构Al3V化合物的内聚性质。计算所得DO22结构Al3V化合物的点阵常数(a=3.72?,c=8.20?)与实验结果一致,体弹性模量(1.3Mbar)与Al3Ti化合物的实验杨氏模最可相比较。计算所得生成热(29±1kcal/mol)与实验值(26.0kcal/mol)相符。
关键词: 相似文献
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在一维局部作用元胞自动机(CA)交通流模型中,引入刹车噪声与产生、消失概率,得到一个完全随机的CA交通流模型.利用平衡自旋理论对该模型的研究表明,当Pin=Pout≠0时,初始密度分布不影响系统的最终状态,求得ρt=0.5;当满足条件Pin+Pb=1与Pin=Pout时,得到简单的“线性”模型,该模型在条件|1-2Pin|=1下,表现出长程相关,导致严重交通“阻塞”的出现.理论结果与计算机实验一致.
关键词: 相似文献
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本文用X射线粉末法测定了Li2K(IO3)3与Li2NH4(IO3)3的晶体结构和原子参数。发现Li3K(IO3)3,Li2NH4(IO3)3与Li2Rb(IO3)3同晶型,属单斜晶系,空间群为P21/α,每个单胞含有四个化合式量。室温的点阵常数分别为α=11.198?,b=11.046?,c=8.254?,β=111.53°,及α=11.327?,b=11.078?,c=8.341?,β=111.87°。讨论了二元化合物的形成与离子半径的关系。
关键词: 相似文献
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The Gaussian wave functional method is applied to a boson system with an array of local nonlinear potentials
cos[βφ(nR)] to study the phase diagram of its ground state. The stable ground state is determined by the renormalized mass μ which is a function of the parameter γ=β2/4φ, the strength of potential α and the potential concentration c. In different cases γ<γ1,
γ1<γ<γ2 and
γ>γ2, μ can have
different multiplicities, the phase diagram in parameter space is thus
depicted. The value γ=γ1 depends on the concentration c,
for c→0, it coincides with that of the single impurity model;
while γ2=2 coincides with the conclusion of the continuous model. 相似文献
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The structural stability, electronic and optical properties of BeH2 under high pressure have been studied using the density functional theory (DFT) employing full potential-linearized augmented plane wave (FP-LAPW) method. The exchange correlation functional has been solved using the generalized gradient approximation. The calculations show that BeH2 becomes unstable upon application of pressure. At a pressure of 29.40 GPa the ground state α-BeH2 transforms to hypothetical phase β-BeH2 and further at a pressure of 53.77 GPa (with respect to the ground state α-BeH2) β-BeH2 transforms to γ-BeH2. In α-BeH2 phase it remains as an insulator while in β-BeH2 phase its behavior becomes metallic. But upon further increase in pressure it becomes a semiconductor in γ-BeH2 phase. Hence the possibility of obtaining high-pressure phases with superconducting properties cannot be ruled out. There occurs a huge equilibrium volume collapse at α- to β-phase transition and relatively smaller volume changes at β- to γ-phase transition. Our obtained value of dielectric constant (3.0) for α-BeH2 is in excellent agreement with earlier reported value (3.1). Also BeH2 shows anisotropic behavior in all three studied phases. 相似文献
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Vikas Nayak 《Phase Transitions》2016,89(5):437-447
In this article, structural and electronic properties of MgH2 have been studied. The aim behind this study was to find out the ground state crystal structure of MgH2. For the purpose, density functional theory (DFT)-based full-potential linearized augmented plane wave (FP-LAPW) calculations have been performed in three different space groups: P42/mnm (α-MgH2), Pa3 (β-MgH2) and Pbcn (γ-MgH2). It has been found that the ground state structure of MgH2 is α-MgH2. The present study shows that α-MgH2 transforms into γ-MgH2 at a pressure of 0.41 GPa. After further increase in pressure, γ-MgH2 transforms into β-MgH2 at a pressure of 3.67 GPa. The obtained results are in good agreement with previously reported experimental data. In all the studied phases, the behavior of MgH2 is insulating and its optical conductivity is around 6.0 eV. The α-MgH2 and γ-MgH2 are anisotropic materials while β-MgH2 is isotropic in nature. 相似文献
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本文从44个缓冷和淬炼Mn-Ga合金摄取了德拜·谢乐照相,并配合了在富Ga部分的差热分析,初步画出了这个系统的相图。这个系统除纯Ga外共有十个相。Mn在Ga中的固溶度是几乎无可觉察的。α相是Ga在α-Mn中的原固溶体,在室温的固溶度为1.95at%Ga。β相在室温的均匀范围为8.6—19.2at%Ga,这是β-Mn结构,因此可看作是β-Mn的固溶体,由于Ga原子无规地替代了部分Mn原子而这个结构得在室温稳定存在。γ相可分成γ1,γ2,γ3,三部分,γ1是面心立方结构,γ2是面心四方结构,γ3是有序的面心四方结构,与Cu-Au系中的CuAuⅠ同型。在室温下稳定的是γ3,均匀范围为37—45at%Ga,而在高温稳定的却总是γ1。从γ1变到γ2,再从γ2变到γ3的变化是二级相变。有序度随Ga含量的递增而递增,随温度的递升而递降。整个γ相可看作是γ-Mn的固溶体,γ-Mn本身是不可能用淬炼的办法在室温获得的。δ相只存在于高温,可看作是δ-Mn的固溶体。由于Ga原子替代了部分Mn原子,因而δ一Mn结构产生了畸变而有序化。ε相是有序的六角密堆积结构,每个晶胞含8个原子,它是在约820℃从γ相同成份地转变而成的,在室温的均匀范围估计为27一30at%Ga。η相在室温约50—60at%Ga处有一宽广的均匀范围。从520到600℃,它经历一多型性变化,转变为λ相。λ相的相区随温度的递升而向富Mn的一边偏移。η和λ结构都很复杂。在富Ga的一边,存在着三个居间相χ,φ和ω,它们是由包析或包晶反应所形成的。ω相的化合式很可能相当于Mn2Ga9或MnGa5,而φ相则与NiHg4同型,在Mn2.3Ga7.7左右有一狭隘的均匀范围。在室温稳定存在的七个居间相中,β,ε,γ3,X和φ是铁磁性的。铁磁性最强的是Ga含量较富的γ3和φ相。我们测量了其中若干合金的饱和磁化强度与居里温度。
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四态叠加多模光场的等幂次N次方H压缩 总被引:5,自引:0,他引:5
根据量子力学中的线性叠加原理,构造了由奇、偶相干态光场所组成的一种新型的四态叠加多模叠加态光场|Ψo,e(4)Ⅲ〉q.它是由多模虚奇相干态和多模虚偶相干态这两者的线性叠加所组成的.利用多模压缩态理论详细研究了态|Ψo,e(4)Ⅲ〉q的等幂次N次方H压缩特性.结果发现:当腔模总数q与压缩次数N的乘积为奇数时,若各模初始相位和qj=1φj、态间叠加几率幅γo、γe以及态间相位差θe-θo等相关参量满足一定的不同条件时,态|Ψo,e(4)Ⅲ〉q可分别呈现以下非经典效应:i)等幂次N次方H压缩;ii)"半相干态"效应. 相似文献
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研究了具有菱方Th2Zn17型结构的Ce2Fe16Al化合物在居里温度TC附近的磁性和磁熵变.实验结果表明,在居里温度附近样品的磁特性符合二级相变规律,样品的居里温度为2758K.通过磁化强度与磁场和温度关系的测量,计算出临界指数β=044±001,γ=130±001,δ=383±001,临界指数β,γ,δ基本满足标度率方程γ=β(δ-1),但偏离三维Heisenberg模型的理论值.Ce2Fe16Al化合物的磁熵变在居里温度处达到峰值,2T外磁场下的最大磁熵变为195J/kg K.
关键词:
Ce2Fe16Al化合物
临界指数
磁熵变 相似文献
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用欧拉有限应变理论分析了埃洛石的冲击Hugoniot实验数据,得到了其低压相和高压相的等熵体积模量K0S及其对压力的一阶导数K′0S。对低压相,在γ=0.43(ρ0/ρ)时,K0S=32.16 GPa,K′0S=7.17;对高压相,在γ=1.0(ρ0/ρ)1.5、且相变能各取579.1 J/g(常压下的值)和1 000 J/g时,K0S、K′0S分别为103.28 GPa 、4.97和95.85 GPa、5.35。根据高压下物性参数的跃变,讨论并分析了其各个相区物质组成的差异。 相似文献
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T. Maitra A. Taraphder A. N. Yaresko P. Fulde 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,49(4):433-439
Motivated by the recent experimental studies on layered ferromagnetic
metallic system GdI2 and its doped variant GdI2Hx we develop a model
to understand their ground state magnetic phase diagram. Based on first
principle electronic structure calculations we
write down a phenomenological model and solve it under certain approximations
to obtain the ground state energy. In the process we work out the phase
diagram of the correlated double exchange model on a triangular lattice
for the specific band structure at hand. 相似文献
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T. Verkholyak A. Honecker W. Brenig 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,49(3):283-287
The Jordan-Wigner transformation is applied to study the ground
state properties and dimerization transition in the J1-J2
XXZ chain. We consider different solutions of the mean-field
approximation for the transformed Hamiltonian. Ground state
energy and the static structure factor are compared with complementary
exact diagonalization and good agreement is found
near the limit of the Majumdar-Ghosh model.
Furthermore, the ground state phase diagram is discussed
within the mean-field theory. In particular, we show that an
incommensurate ground state is absent for large J2 in a fully
self-consistent mean-field analysis. 相似文献