六角密堆结构的Mbius变换及镁的对势

提出并证明了一个适用于六角密堆(hcp)结构的Mbius变换公式.从晶体中原子的结合能出发，利用这个公式可以得到具有hcp结构的晶体中原子间的相互作用对势.作为例子，利用这一方法计算了镁的对势. 关键词：     

NaZn13型Fe基化合物的结构和热力学性质研究

利用Chen-Mbius晶格反演获得的原子间相互作用势,对NaZn13型Fe基金属间化合物进行原子级模拟研究.计算结果表明,Si原子和Co原子均优先占据96i晶位,Si原子和Co原子替代Fe原子后晶体平均结合能降低.随着Co含量的增加,LaFe13-x-yCoySix和NdFe13-x-yCoySix的晶格参数逐渐降低.声子态密度中,稀土原子主要激发低频模,Si原子主要激发高频模.LaFe11.5-yCoySi1.5化合物的德拜温度随Co含量的增加而增高.     

NaZn13型Fe基化合物的结构和热力学性质研究

利用Chen-Mbius晶格反演获得的原子间相互作用势,对NaZn₁₃型Fe基金属间化合物进行原子级模拟研究.计算结果表明,Si原子和Co原子均优先占据96i晶位,Si原子和Co原子替代Fe原子后晶体平均结合能降低.随着Co含量的增加,LaFe_13-x-yCo_ySi_x和NdFe_13-x-yCo_ySi_x的晶格参数逐渐降低.声子态密度中,稀土原子主要激发低频模,Si原子主要激发高频模.LaFe_11.5-yCo_ySi_1.5化合物的德拜温度随Co含量的增加而增高. 关键词： 晶格反演 原子间相互作用势 热力学性质 磁致冷材料     

腔量子电动力学系统中耦合三原子的纠缠特性

研究了三个全同二能级原子与单模腔相互作用系统中原子间的三体纠缠特性.考虑原子间存在相互耦合,并且腔场处于弱相干态的情况,通过数值计算给出了纠缠量的演化曲线,讨论了原子间耦合强度和弱相干场强度对三体纠缠的影响.研究结果表明:随弱相干场强度增强,原子间的三体纠缠增强;相反,随原子间耦合系数增大,原子间三体纠缠减弱.     

金和银的晶格反演势的构建及应用

如何确定精确的原子间作用势一直是模拟计算的重要基础问题. 以面心立方金属金和银为对象, 采用第一性原理方法, 分别得到金和银的晶格内聚能-原子距离曲线及基态原子能曲线. 根据陈-莫比乌斯(Chen-Möbius)晶格反演理论和自编程序, 得到了精确的反演对势曲线. 对该曲线进行拟合, 通过比较不同势函数的拟合结果, 提出了双指数型的势函数解析式, 并得到具有全局性且高精度的拟合效果. 为了验证反演势的有效性, 利用反演势结果计算了金和银的声子谱并与Sutton-Chen提出的嵌入原子势和第一性原理计算得到的声子谱做比较. 分析表明, 反演势能够合理反映原子间的相互作用. 最后, 利用得到的结果, 计算了金和银的热膨胀系数和弹性模量等物理量, 计算结果与实验数据基本符合, 表明构建的金和银的反演势是准确有效的.     

铁基氟化物超导体SrFe_(1-x)Co_xAsF(x=0,0.125)声子特性的第一性原理计算研究

采用基于第一性原理的平面波赝势方法,计算了铁基氟化物及其钴掺杂超导体SrFe1-xCoxAsF(x=0,0.125)在四方非磁态与正交条纹反铁磁态下的声子谱(声子色散曲线、声子态密度)及电-声子耦合常数.计算发现:条纹反铁磁相互作用下的自旋-声子耦合效应强于电-声子耦合作用使声子谱的宽度减小;自旋效应使声子的有效质量增加导致条纹反铁磁态下Fe原子与As原子的耦合振动频率减小.另外,掺杂和自旋效应是提高电-声子耦合常数的两个有效方法,但计算所得超导转变温度远小于实验测量值,表明铁基超导电性非简单的电-声子耦合配对机理.     

抛物量子阱中束缚极化子的极化势和结合能

利用改进的Lee-Low-Pines(LLP)方法,用变分法计算了无限深抛物量子阱中同时考虑与体纵光学声子和界面纵光学声子相互作用的束缚极化子的极化势和结合能.数值计算得出:阱宽较大时极化势很小,阱宽较小时极化势较大,所以对于较窄的抛物阱必须考虑极化势.对于给定阱宽的抛物阱,随着远离阱中心极化势迅速减小,当到达阱的界面附近极化势又开始增大.阱宽较小时,束缚极化子的结合能随着阱宽L的增大而急剧减小;阱宽较大时,结合能减小的非常缓慢,最后接近体材料中的三维值.     

固体中的原子间相互作用势

近年来，原子间相互作用势广泛应用物理、化学、材料科学中，文章综合评述了金属和半导体中原子间相互作用势研究的发展状况以及各种势函数的范围和存在的总理２，总结了近年来金属合金以及半导体化合物中原子间相互作用势的应用情况，并讨论了固体中原子间相互作用势的发展方向。     

层状铁电晶体MBiP2X6(M=Cu,Ag;X=S,Se)拉曼光谱的第一性原理研究

基于密度泛函理论的第一性原理计算,本文首次研究了过渡金属卤代磷酸酯MBiP2X6(M=Cu,Ag;X=S,Se)三维晶体和二维晶体的声子色谱和拉曼散射谱.以反铁电晶体AgBiP2Se6为例,根据声子谱的计算结果,验证了低温反铁电相是动力学稳定的.结合声子总态密度可以得到:声子谱光学支的低频部分主要来源于阳离子M+和Bi...     

原子与热库相互作用系统中的三体纠缠特性

利用Ket-Bra纠缠态方法,求解了原子与热库相互作用系统中的密度矩阵主方程,得到了密度矩阵的演化表达式.考虑三个二能级原子独立与热库相互作用的情况,利用负本征值度量三体纠缠,研究了系统中原子间的三体纠缠特性.采用数值计算方法,讨论了热库平均光子数和原子自发辐射率对原子间三体纠缠特性的影响.研究结果表明:随原子自发辐射率和热库平均光子数的增大,原子间的三体纠缠衰减加快.     

Three-body interaction and phonon dispersion relations in aluminium

Based on an ab initio cohesive energy calculation and a model of three-body interaction, the pair potential can be calculated using the Möbius inversion theorem in the theory of numbers. Then the atomic force constants and the phonon dispersion for A1 are evaluated both with and without three-body interaction. Compared with experiments, the results show that taking the three-body interaction into account considerably improves the dispersions. Contrary to previous work, the method for calculating the atomic force constants and phonon dispersions presented here is simple, with only two adjustable parameters.     

Phonon dispersion for the bcc metals Mo and Cr

In this paper the phonon dispersion for the bcc metals Mo and Cr is calculated based on the pair potentials obtained from cohesive energies and the Slater-Kirkwood- type three body interaction. In the calculation of the pair potentials the Möbius transform in the number theory is used and the cohesive energy is evaluated by the LMTO method. The results show a good agreement with inelastic neutron scattering data and indicate that the three-body interaction is necessary to account for the phonon dispersion.     

First-principles lattice dynamics,thermodynamics, and elasticity of Cr2O3

We present the calculation of the lattice dynamics of chromia (Cr₂O₃), a typical Mott–Hubbard insulator, employing the first-principles density functional theory plus U approach. We first report the phonon dispersions at the theoretical equilibrium volume. Then the phonon density-of-states is calculated as a function of volume. Finally, the atomic volume, heat capacity, linear thermal expansion coefficient, bulk modulus, Grüneisen constant, and elastic constants are calculated as functions of temperature.     

高压下FCC相金属氢结构稳定性和非谐效应的理论研究

利用第一性原理分子动力学方法研究金属氢体系的非简谐效应, 给出金属氢的声子谱, 讨论金属氢声子谱的温度效应。计算得到氢的同位素氕、氘和氚的FCC相在非零温下的声子谱, 不同温度下的声子谱对比发现零温下3.6 TPa为热力学稳定的临界压强点, 而有限温度下(100 K)临界压强点降到2.8 TPa, 非简谐效应显著地改变了体系的结构稳定性和声子振动性质。     

The transverse electron scattering response function of 3He

Results on the transverse response function R _T (q,ω) of ³He obtained within the Lorentz integral transform [LIT] [1] method are presented. The response is calculated using the BonnRA nucleon-nucleon potential [2], the Tucson-Melbourne [3] three-body force, and the Coulomb potential for various momentum transfers. The results are compared with available data.     

Lattice dynamics of some binary alloys

Summary The phonon dispersion frequencies for Cu₃Au, Cu₃Zn and Ni₃Fe alloys have been calculated using the model potential approach. The contribution of a short-range three-body interaction to the dynamical matrix has also been included in the present study. The theoretically computed phonon dispersion curves of these alloys are found to be in good agreement with the experimental data.     

Compton profiles and nesting of Fermi surfaces for B2-TiNi and B2-TiPd

The band structures of the shape memory alloys B2-TiNi and B2-TiPd are calculated by the full potential linearized augmented plane wave method with the local density approximation. The theoretical Compton profiles for B2-TiNi and B2-TiPd are calculated. In addition, the three-dimensional (3D) occupation number densities obtained by Lock-Crisp-West (LCW) analysis are presented for the first time. These 3D occupation number densities are in good agreement with the Compton scattering experiment for TiNi. Both shape memory alloys are based on martensitic transformation, which is caused by soft phonons. The charge-density wave is created by nesting of Fermi surfaces, which leads to phonon softening. To examine the nesting vectors quantitatively, we calculate the generalized susceptibility χ(q). χ(q) shows peaks at 0.315[110]2π/a and 0.4[111]2π/a for TiNi and at 0.275[110]2π/a and 0.395[111]2π/a for TiPd. Although the nesting vector in the [110] direction agrees with that from the phonon experiment, the nesting vector in the [111] direction differs from that in the experimental results.     

Lattice dynamics of cubic PbTiO3 by inelastic neutron scattering

High-temperature dispersion relations of the phonon modes in a cubic PbTiO₃ single crystal have been investigated along the [ξ 0 0] and [ξ ξ 0] directions by inelastic neutron scattering. Above T _c, the phonon dispersions are only temperature-dependent close to the Brillouin zone centre where the mode softening comes through. The measurements indicate large cubic anisotropy of the elastic tensor and relatively low anisotropy of the soft mode dispersion. The differences from an earlier inelastic neutron scattering study are discussed.     

Low Energy D(p, p)D Elastic Scattering Including Coulomb Force

The motivation of this paper is to obtain the three-body amplitudes for the Coulomb potential plus a nuclear force in momentum space. Not only the two-body off-shell nuclear amplitude but also the two-body off-shell Coulomb amplitude is important in the three-body calculation. For calculating the Coulomb amplitude, the modified Coulomb potential whose Fourier transformation is analytically equivalent to the pure configuration space Coulomb potential, is introduced. In addition, the decisive screening range parameter is also utilized instead of the screening range. The modified Coulomb potential plus the parameter is called decisive modified Coulomb potential. The three-body proton-deuteron elastic scattering is calculated by using the proper two-body off-shell amplitude for the decisive modified Coulomb potential.     

Lattice dynamics in mixed valent Rare Earth compounds

In the frame of a single coherent picture for the electron lattice interactions in mixed valent Rare Earth compounds, the phase diagrams and phonon dispersions are studied. Our model is introduced on a microscopic level and discussed in detail. The mechanism of the phase transition and the role of the lattice is illuminated and various properties are considered in a model calculation. Anomalies in the phonon dispersions of Sm_1–x Y _x S, which have recently been found, find a satisfying explanation.