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1.
A.K. Kushwaha 《理论物理通讯》2008,50(6):1422-1426
A rigid-ion model is used to calculate the force constants and effective
dynamical charges of sulphide and selenide spinels. The Raman and infrared
phonon modes of normal cubic sulphide spinels MCr2Se4
(M = Mn, Co, Fe, Hg, Zn, and Cd) and selenide spinels MCr2Se4
(M = Hg, Zn, and Cd) are calculated at the first Brillouin zone-centre using above model. The
significant outcome of the present work is (i) the interatomic interaction
between Cr-S (Se) dominates over the
Cr-S(Se) and S-S(Se-Se) type of
interatomic interactions, (ii) the effective dynamical charges of the
bivalent metal ions are nearly zero, and (iii) the selenide spinels are less
ionic than the sulphide spinels and the ionicity decreases as
MnCr2S4 >
FeCr2S4 >
CoCr2S4 > and
CdCr2C4 >
ZnCr2C4 >
HgCr2C4
(C = S and Se). The zone-center phonon frequencies, calculated using these parameters, are
found to be in very good agreement with the observed results. 相似文献
2.
First-principles calculations,which are based on the plane-wave pseudopotential approach to density functional perturbation theory within the local density approximation,have been performed to investigate the structural,lattice dynamical and thermodynamic properties of zinc blende(B3) structure magnesium chalcogenides:MgS,MgSe and MgTe.The results of ground state parameters and phonon dispersion are compared and agree well with the experimental data available and other calculations.We obtain the change of Born effective charge and LO-TO splitting under hydrostatic pressure.Finally,by the calculations of phonon frequencies,some thermodynamic properties such as the entropy,heat capacity,internal energy,and free energy are also successfully obtained. 相似文献
3.
碳纳米管的结构、对称性及晶格动力学 总被引:7,自引:8,他引:7
本文介绍了单层碳纳米管的结构,对称性和晶格动力学,描述了单层碳纳米管结构的表征方式,碳纳米管的晶格振动模的对称性分类和声子色散曲线。 相似文献
4.
Cristina Toninelli Giulio Biroli Daniel S. Fisher 《Journal of statistical physics》2005,120(1-2):167-238
Kinetically constrained lattice models of glasses introduced by Kob and Andersen (KA) are analyzed. It is proved that only two behaviors are possible on hypercubic lattices: either ergodicity at all densities or trivial non-ergodicity, depending on the constraint parameter and the dimensionality. But in the ergodic cases, the dynamics is shown to be intrinsically cooperative at high densities giving rise to glassy dynamics as observed in simulations. The cooperativity is characterized by two length scales whose behavior controls finite-size effects: these are essential for interpreting simulations. In contrast to hypercubic lattices, on Bethe lattices KA models undergo a dynamical (jamming) phase transition at a critical density: this is characterized by diverging time and length scales and a discontinuous jump in the long-time limit of the density autocorrelation function. By analyzing generalized Bethe lattices (with loops) that interpolate between hypercubic lattices and standard Bethe lattices, the crossover between the dynamical transition that exists on these lattices and its absence in the hypercubic lattice limit is explored. Contact with earlier results are made via analysis of the related Fredrickson--Andersen models, followed by brief discussions of universality, of other approaches to glass transitions, and of some issues relevant for experiments. 相似文献
5.
Herein, the spin dynamics for various magnetic configurations arranged on a Kagome lattice is investigated. Using a Holstein–Primakoff expansion of the isotropic Heisenberg Hamiltonian with multiple exchange parameters, the development and evolution of magnetic Dirac nodes with both anisotropy and magnetic field are examined. From the classical energies, the phase diagrams for the ferromagnetic (FM), antiferrimagnetic (AfM), and the 120° phases are shown as functions of J1, J2, J3, and anisotropy. Furthermore, the production of bosonic Dirac and Weyl nodes in the spin-wave spectra is shown. Through frustration of the magnetic geometry, a connection to the asymmetric properties of the Kagome lattice and the various antiferromagnetic configurations is discerned. Most interesting is the 120° phase, which does not have Dirac nodes when considering only J1 due to the formation of an analogous antiferromagnetic honeycomb lattice, but gains Dirac symmetry with next-nearest neighbor interactions. Additionally, the presence of flat modes that are characteristic of cluster excitations is shown. Further study of external frustrations from a magnetic field and anisotropy reveals a tunability of the exchange interactions and nodal points. 相似文献
6.
将高精度的二氧化碳状态方程与气液两相流格子Boltzmann方法中的伪势模型耦合,研究微通道内二氧化碳气液两相流动的界面动力学行为,包括二氧化碳气泡和液滴的分裂、合并、变形,以及气液两相二氧化碳在演化过程中的质量交换.研究发现:当分裂和合并行为达到平衡,并且两相之间不发生质量交换时流动达到稳态.稳态时的流型主要依赖于表面张力,惯性力,管道的润湿性,以及初始体积分数.当表面张力较大时,微通道内形成的二氧化碳气泡或液滴会收缩成圆形,此时二氧化碳气泡或液滴会堵塞微通道,形成段塞流;随着表面张力的减小,形成的气泡或液滴不容易收缩,在微通道内更容易发生变形,出现泡状流或环状流.当壁面润湿性为强疏水性时,二氧化碳在微通道中的流动为环状流,其它润湿性下,流型为段塞流.体积分数较小时,二氧化碳两相流动的流型为段塞流,体积分数较大时,流型为环状流. 相似文献
7.
通过求解差分方程,推导了纳米晶体线的晶格动力学格林函数,分析了其晶格振动,并推导了声子数表象中的原子位移及晶格振动哈密顿公式.研究结果表明,纳米晶体线的晶格振动能带分裂为一系列的子带,格波只能沿纳米晶体线的纵向传播,沿纳米晶体线的横截面只存在驻波. 相似文献
8.
We report here measurements of the phonon density of states and the lattice dynamics calculations of strontium tungstate (SrWO4). At ambient conditions this compound crystallizes to a body-centred tetragonal unit cell (space group I41/a) called scheelite structure. We have developed transferable interatomic potentials to study the lattice dynamics of this
class of compounds. The model parameters have been fitted with respect to the experimentally available Raman and infra-red
frequencies and the equilibrium unit cell parameters. Inelastic neutron scattering measurements have been carried out in the
triple-axis spectrometer at Dhruva reactor. The measured phonon density of states is in good agreement with the theoretical
calculations, thus validating the interatomic potential developed.
相似文献
9.
10.
应用格子Boltzmann三维模型,对双气泡在静水中的运动进行数值研究.采用八点差分和十八点差分格式分别求解一阶▽φ和二阶▽2φ可以有效避免气液密度比过大造成的数值不稳定问题.结果表明:当两个相同直径的气泡在上升时,位置靠上的气泡形状变化像单气泡上升一样,而位置靠下的气泡会受到前一个气泡尾迹的影响,并有很明显的形状变化.当两个气泡直径不同时,不管初始位置如何,大气泡总会对小气泡造成强烈的影响. 相似文献
11.
12.
C. Chris Wu 《Journal of statistical physics》2002,106(1-2):369-373
We consider the nature of spin flips of zero-temperature dynamics for ferromagnetic Ising models on the triangular lattice with nearest-neighbor interactions and an initial configuration chosen from a symmetric Bernoulli distribution. We prove that all spins flip infinitely many times for almost every realization of the dynamics and initial configuration. 相似文献
13.
We have studied lattice gases with a particle-conserving dynamic rule that involves two principal parameters. One of them has two limiting values that correspond, respectively, to a large, saturating constant field, which induces a positive particle current, and to a random field (zero net current). Varying the other parameter, either particle attractions or repulsions perpendicular to the field are simulated. The nature of ordering is shown to be independent of the value for the field parameter. In particular, the two indicated limiting cases of the latter lead to the same order-parameter critical behavior, consistent with 1/3, in the presence of a linear interface for attractions in two dimensions. Some qualitative features of the time relaxation are briefly described. 相似文献
14.
DENG Min-Yi SHI Juan CHEN Rui-Xiong KONG Ling-Jiang LIU Mu-Ren 《理论物理通讯》2007,48(4):725-728
We investigated the dynamics of the simple spiral waves of the Se/kov reaction-diffusion system with the Lattice Boltzmann method. The results of computer simulation lead to the conclusion that the trajectory of the spiral tip is a small circle, the wavelength and the period decay exponentially when the value of parameter b increases; and the relation between the wavelength and the period is λ ∝ T1/2, which is qualitatively the same as that obtained by Ou-Yang Qi from Belousov-Zhabotinsky reaction system. 相似文献
15.
James E. Broadwell 《Journal of statistical physics》2001,103(5-6):1125-1136
A simple lattice gas model, a microscopically reversible cellular automaton, is described and shown to exhibit thermodynamic irreversibility in processes similar to those in real gases. The model, which has no random elements, develops a long-lasting equilibrium state within a Poincaré cycle. This state is an attractor resulting from the nonlinear nature of the collective particle collisions and motions. The results illustrate how the Second Law of Thermodynamics applies to real systems governed by reversible microscopic dynamics. 相似文献
16.
A short‐range force constant model (SRFCM) has been applied to investigate the Raman and the infrared wavenumbers in Nd2BaZnO5 in its tetragonal phase of space group I4/mcm. Calculations of zone‐center phonons are made with five stretching and five bending force constants. All the Raman and infrared values are then assigned to their corresponding modes. Two Raman modes are reassigned on the basis of group theoretical calculations. The calculated Raman wavenumbers exhibit good agreement with the observed values. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
17.
18.
采用有效多松弛时间-格子Boltzmann方法(Effective MRT-LBM)数值模拟了微尺度条件下的振荡Couette和Poiseuille流动. 在微流动LBM中引入Knudsen边界层模型,对松弛时间进行修正. 模拟时平板或外力以正弦周期振动,Couette流中考虑了单平板振动、上下板同相振动这两类情况. 研究结果表明,修正后的MRT-LBM模型能有效用于这类非平衡的微尺度流动模拟;对于Couette流,随着Kn数的增大,壁面滑移效应变得越明显. St越大,板间速度剖面的非线性特性越剧烈;两板同相振荡时,若Kn,St均较小,板间流体受到平板拖动剪切的影响很小,板间速度几乎重叠在一起;在振荡Poiseuille流动中,St数增大到一定值时,相位滞后现象减弱;相对于Kn数,St数对振荡Couette 和Poiseuille流中不同位置处速度相位差的产生有较大影响.
关键词:
格子Boltzmann方法
有效MRT模型
Knudsen层
振荡流 相似文献
19.
Vitaly A. Shneidman 《Journal of statistical physics》2003,112(1-2):293-318
A lattice gas with non-conserved spin flip dynamics (of both non-Glauber and Glauber types) is considered at TT
c
, the critical temperature. For arbitrary supersaturation, S, a general expression for the inverse of the nucleation rate along the lowest energy path is derived. The exponential part is identical to the one by Neves and Schonmann [Commun. Math. Phys.
137:20 (1991)]. The preexponential can be expressed in terms of elliptic theta-functions for small S, and in the limits, respectively, of ST/ or ST/ (– being the nearest-neighbor interaction energy), elementary versions of the general expression are further obtained. The preexponential has a smooth component, as well as small-scale modulations which are approximately periodic in the inverse supersaturation. For ST/, the smooth part is proportional to
, in contrast to the zero-T limit where it is linear in S. The latter limit becomes apparent only at extremely low temperatures which are cubic in S. 相似文献
20.
Our lattice dynamics simulation of Xe-hydrate with four-site TIP4P
oxygen-shell model can accurately reproduce each peak position in
the inelastic incoherent neutron scattering spectrum at the acoustic
band (below 15\,meV) and yield correct relative intensity. Based on
the results, the uncertain profile at $\sim $6\,meV is assigned to
anharmonic guest modes coupled strongly to small cages. Blue shift
is proposed in phonon dispersion sheet in the case of anticrossing
and found to be an evident signal for guest--host coupling that
explains the anomalous thermal conductivity of clathrate hydrate. 相似文献