具有在位势的一维双原子链中杂质引起的对称局域模

对具有在位势且含杂质的一维双原子链的晶格振动方程组进行求解,得到了局域振动的解析解,给出了在位势对局域振动影响的基本特征,并简要讨论了对称局域模的存在形式.     

具有在位势的一维双原子链晶格振动的长声学波图像

通过数值求解具有在位势的一维双原子链晶格振动的运动方程组,给出了具有不同大小在位势的长声学波振动模图像,直观展示出在位势使原胞中两种原子的振动位移不同,并且随在位势的增大,振动位移之差显著增大.     

具有在位势的一维双原子链晶格振动的色散关系

在简谐近似下,求解具有在位势的一维双原子链晶格振动运动方程,得到了具有在位势的晶格振动的色散关系.在位势使色散关系声频支在布里渊区中心的振动频率不再为零,并且随在位势的增大而增大.对于原子之间相互作用势不随在位势大小变化的情况下,晶格振动的色散关系的频隙随在位势的增大而变宽.讨论了原子链由只有在位势的不连续极限(AC极限),通过在位势逐渐减弱而原子间相互作用势逐渐增强,最后演变到只有原子间相互作用势的原子链的情况.随着在位势减弱和相互作用势增强,色散关系的频隙由AC极限的孤立轻、重原子简谐振动频率之差逐渐变化到通常的无在位势的色散关系频隙.     

在位势对于一维双原子链晶格振动长声学波的影响

根据声学模的定义,明确了具有在位势的一维双原子链的晶格振动不存在声学模,讨论了具有在位势的一维双原子链晶格振动的低频支长波模振动图像,得到原胞中两种原子运动的振幅不再一致,低频支长波模不再是原胞质心的运动,且两种原子运动的振幅比随在位势的增大而单调增大.     

次近邻近似下具有在位势的一维双原子链中杂质引起的局域振动

考虑原子间次近邻相互作用,讨论了具有在位势的一维双原子链中杂质引起的局域振动,得到次近邻互作用力、在位势共同作用下局域模的存在条件及振动的基本特征.     

一维单原子链中杂质引起的局域振动模

讨论了一维单原子链中杂质引起的晶格局域振动模和局域振动图像,分析了杂质质量和杂质近邻力常数对振动模的影响,通过数值求解晶格振动运动方程组．给出了局域振动模关于杂质质量和杂质近邻力常数分布的相图;分析了含杂质晶格振动模频率相对于完整晶格振动模频率的变化。     

次近邻电子跳跃对孤子的电子束缚态和孤子附近局域模的影响

从SSH模型出发,考虑电子次近邻跳跃的影响,研究了聚乙炔中孤子的电子束缚态和孤子附近的局域振动模。结果发现:1.电子能谱中的电子-空穴对称性消失;2.孤子的电子束缚态的数目和位置发生了变化,且与孤子的类型有关;3.孤子附近出现了一个新的局域振动模G₆;4.次近邻电子跳跃改变了局域模的频率,增强了局域模的局域性。 关键词：     

一维双原子链中杂质引起的局域振动模

对含杂质的一维双原子链,在链中所有原子之间近邻相互作用力常数均相等的情况下,数值求解晶格振动的运动方程组,得到不同局域振动模的振动图像和产生条件,给出了局域模关于杂质原子质量和原胞中两种晶格原子质量比分布的相图．     

一维高分子链中点缺陷引起的局域模

将聚苯胺等一类聚合物简化成一维复式线性链,讨论了这一类聚合物仅含一个点缺陷时的振动模.考虑到点缺陷附近弹性恢复力常数的变化,预期了局域模的出现,说明了模的局域化程度,包括模的频移及振动本征矢的分布情况与质量缺陷程度、力常数改变程度的关系.     

不变本征算符方法求解含不同在位势的一维双原子链的色散关系

本文运用全量子化的不变本征算符方法, 求解了含有不同简谐在位势的一维双原子链模型, 得到其色散关系并讨论了不同在位势系数之比和力常数对于色散关系高频支和低频支的影响, 分析发现在位势的存在使得低频支和高频支的频谱都有一定程度的抬高; 在一定的条件下, 布里渊区边界的高频支与低频支存在交点, 意味着在某些在位势下, 高频支与低频支的频隙为零. 关键词： 在位势 一维双原子链 不变本征算符方法 色散关系     

S2O分子的局域势能面和振动光谱的解析

用MRCISD和MRPT2计算了S2O分子的局域势能面，对计算点完成了力场多项式拟合和振动组态相互作用的计算.然后，对其基态(1A′)和激发态(1A′)的振动模式和振动光谱进行分析.通过调节力常数，势能面得到进一步改进.与已有的实验能谱数据进行比较，基态与激发态的均方差分别为3852cm-1和644cm-1. 关键词： S2O 势能面 能谱 MRCISD MRPT2     

Electronic structure studies of CeAgSb2

The electronic band structure of CeAgSb₂ has been calculated using the self-consistent full potential nonorthogonal local orbital minimum basis scheme based on the density functional theory. We investigated the electronic structure with the spin-orbit interaction and on-site Coulomb potential for the Ce-derived 4f orbitals to obtain the correct ground state of CeAgSb₂.     

Discrete breathers in a two-dimensional Morse lattice with an on-site harmonic potential

Two-dimensional discrete breathers in a two-dimensional Morse lattice with on-site harmonic potentials are investigated. Under the harmonic approximation, the linear dispersion relations for the triangular and the square lattices are discussed. The existence of discrete breathers in a two-dimensional Morse lattice with on-site harmonic potentials is proved by using local inharmonic approximation and the numerical method. The localization and amplitude of two-dimensional discrete breathers correlate closely to the Morse parameter a and the on-site parameter κ.     

Thermal Transport in One-Dimensional FPU-FK Lattices

Thermal transport in the FPU model with FK on-site potential is studied by using fourth-order Runge-Kutta algorithm. The heat flux, local temperature profile, and heat conductivity are simulated and analyzed. It is found that temperature gradient scales behave as N^-1 linearly. The divergence of heatconductivity κ with system size N is in term of κ∝ N^α with α=0.44. It is shown that thermal transport is mainly dependent on the FPU nonlinear and the FK interactions.     

Phonon transmission and thermal conductance in one-dimensional system with on-site potential disorder

The role of on-site potential disorder on phonon transmission and thermal conductance of one-dimensional system is investigated. We found that the on-site potential disorder can lead to the localization of phonons, and has great effect on the phonon transmission and thermal conductance of the system. As on-site potential disorder W increases, the transmission coefficients decrease, and approach zero at the band edges. Corresponding, the thermal conductance decreases drastically, and the curves for thermal conductance exhibit a series of steps and plateaus. Meanwhile, when the on-site potential disorder W is strong enough, the thermal conductance decreases dramatically with the increase of system size N. We also found that the efficiency of reducing thermal conductance by increasing the on-site potential disorder strength is much better than that by increasing the on-site potential?s amplitude.     

Assessment of Timoshenko Beam Models for Vibrational Behavior of Single-Walled Carbon Nanotubes Using Molecular Dynamics

In this paper, we study the flexural vibration behavior of single-walled carbon nanotubes (SWCNTs) for the assessment of Timoshenko beam models. Extensive molecular dynamics (MD) simulations based on second-generation reactive empirical bond-order (REBO) potential and Timoshenko beam modeling are performed to determine the vibration frequencies for SWCNTs with various length-to-diameter ratios, boundary conditions, chiral angles and initial strain. The effectiveness of the local and nonlocal Timoshenko beam models in the vibration analysis is assessed using the vibration frequencies of MD simulations as the benchmark. It is shown herein that the Timoshenko beam models with properly chosen parameters are applicable for the vibration analysis of SWCNTs. The simulation results show that the fundamental frequencies are independent of the chiral angles, but the chirality has an appreciable effect on higher vibration frequencies. The SWCNTs is very sensitive to the initial strain even if the strain is extremely small.