含有格点势的一维Fibonacci链热传导性质的研究

用传输矩阵的方法,研究了格点势(on-site势)对一维Fibonacci链的热传导性质(透射系数、Lyapunov指数及热导率κ)的影响.研究结果表明:当固定原子质量比和力作用常数比时,随着格点势的增大,低频区域的透射系数减小,对应的Lyapunov指数增大,透射谱向高频方向移动.同时,格点势越大,同样大小的体系对应的κ越小,当格点势足够大时,κ会趋近零.在热导率κ对振动频率ω²作图中,κ呈现台阶式缓慢上升的趋势,且在高频     

PH, PD和PT分子常数理论研究

采用内收缩多参考组态相互作用(MRCI)方法和包含Davidson修正(+Q) 的MRCI方法结合相关一致基aug-cc-pV5Z研究了PH (X³Σ^-, a¹Δ和A³∏)分子的势能曲线. 在同位素质量识别的基础上对势能曲线进行拟合, 得到PH, PD和PT分子各个电子态的光谱常数(T_e, R_e, ω_e, ω_ex_e, α_e和 B_e). 通过与已有实验数据的比较发现, 本文的结果与实验结果非常一致. 对于PH, PD和PT分子的Σ^-电子态, 计算得到了J = 0时的前12个振动态. 对于每一个振动态, 还分别计算了它的振动能级、惯性转动常数和离心畸变常数. 与其他理论结果和实验数据进行比较可知, 本文的结果更精确、更完整. 文中PD和PT分子的光谱常数和分子常数均属首次报导.     

多声子跃迁的Franck-Condon因子

在位形座标中,表示电子态u和v的两条抛物线水平方向位移(2S)1/2,垂直方向位移pohω。选取横座标(无量纲位形z)单位,使极小值位于原点的抛物线在z=±1处纵座标为0点振动能1/2hω。S即黄-李-Пеяар因子。     

7Li2(X1Σ+g)分子的振动能级、转动惯量及离心畸变常数

使用密度泛函理论B3LYP和B3P86，以及组态相互作用方法CCSD(T)和QCISD, 利用多个基组对⁷Li₂(X¹Σ⁺_g)分子的平衡核间距(R_e)、谐振频率(ω_e)和离解能(D_e)进行了计算, 发现在CCSD(T)/cc-PVQZ理论水平下得到的结果(R_{e相似文献}   

宽带三倍频混频过程的群速匹配关系

基于非线性耦合波理论分析了三倍频过程中群速度之间的关系，推导出三波混频条件下的群速匹配关系式.对超短脉冲在Ⅱ类KDP晶体中的混频过程进行了模拟分析，结果表明：当三波(基波ω，谐波2ω和3ω)的群速度满足该匹配关系式时，三倍频(3ω)的带宽和转换效率均可达最大值；而随着三波群速度对该关系式的偏离逐渐增大，带宽变窄、转换效率下降.导出的三波群速匹配关系式对寻找合适的色散晶体和选择有效的匹配措施、实现宽带三次谐波转换具有指导意义.     

Kerr效应和虚光场效应对三能级原子-场系统原子占居态几率的影响

研究类克尔介质中非旋波近似下三能级原子与场相互作用系统的原子占居态几率的时间演化;讨论了光场频率ω及类克尔介质常量x对原子占居态几率的影响。结果表明:虚光场的作用使原子占居态几率的时间演化曲线中出现量子噪音,而Kerr介质效应会抑制量子噪音的产生;原子吸收率随x的增大而降低;系统的粒子数反转随x的增大明显减弱,但随ω的增大有所增强。     

两耦合半无限超晶格中的局域界面声子-极化激元

采用转移矩阵方法，研究了含结构缺陷层的两耦合半无限超晶格(GaAs/AlAs)中的局域界面声子-极化激元模性质. 研究发现，含不同介电特性的缺陷超晶格结构中的局域界面声子-极化激元模在剩余射线区［ω_TO, ω_LO］的分布情况与数量存在不同，而且反对称模表现出不同的特征. 文中着重研究了缺陷层介电常数与角频率无关的缺陷超晶格，发现该结构中的局域界面声子-极化激元模对组分层的排列顺序与厚度、缺陷层的厚度以及横向波数有着不同程度的依赖.     

调控电磁感应透明气体折射率实现可控光子带隙结构

提出了电磁感应透明(EIT)介质的一个新的相干操纵应用：控制电磁感应透明气体折射率实现可控光子带隙结构. 将一定密度的EIT原子气体充入以砷化钾为背景的椭圆孔柱中，计算表明该三角晶格排列椭圆柱光子晶体的光子带隙随外控制场而变. 通过调控自发辐射率、无辐射衰变率、控制光Rabi频率、原子数密度等外参数以及椭圆结构几何参数，在高频率区域得到了大小约0.0503ω_e(ω_e=2πc/a)的完全光子带隙.     

非旋波近似下类克尔介质中“单模光场-受激三能级原子”系统的光子统计演化分析

本文研究了非旋波近似下类克尔介质对“单模光场-受激三能级原子”系统的光子统计演化特性的影响.数值计算的结果表明:类克尔介质的作用直接影响着受激辐射场的平均光子数< n(t) >的Rabi振荡的幅度和频率;而虚光场的影响则表现为受激辐射场的量子噪音,它与激发场强的变化及场与介质的耦合程度密切相关.另外,本文还对< n(t)>进行了频谱分析,结果发现该非线性系统存在着一系列高次谐波;并且,各高次谐波成分和振幅的变化情况完全依赖于激发场强及与介质的耦合程度.     

基于移位算子时域有限差分的色散薄层节点修正算法

提出了一种时域有限差分（FDTD）计算中色散介质薄层问题处理的新算法.对于厚度小于一个元胞尺度的电小尺寸色散介质薄层问题,采用将元胞内电位移矢量和磁感应强度加权平均的方法,求得薄层所在元胞内修正点处的等效介质参数.然后根据常见色散介质模型,包括Debye模型、Lorenz模型、Drude模型等,介电常数和磁导率可以表示为jω分式多项式的特点,结合频域到时域的转换关系（即用/t代替jω）和移位算子方法得到了修正点处的时域本构关系,进而获得时域递推计算式.数值结果表明,该方法具有通用、节省计算时间、节省内存和计算精度良好等优点.     

Quantum computation with vibrationally excited polyatomic molecules: effects of rotation,level structure,and field gradients

Accurate rotation–vibration energy levels and transition dipoles of the molecule thiophosgene are used to model the execution of quantum gates with shaped laser pulses. Qubits are encoded in 2 ⁿ vibrational computing states on the ground electronic surface of the molecule. Computations are carried out by cycling amplitude between these computing states and a gateway state with a shaped laser pulse. The shaped pulse that performs the computation is represented by a physical model of a 128–1024 channel pulse shaper. Pulse shapes are optimized with a standard genetic algorithm, yielding experimentally realizable computing pulses. The robustness of optimization is studied as a function of the vibrational states selected, rotational level structure, additional vibrational levels not assigned to the computation, and compensation for laser power variation across a molecular ensemble.     

Laser-induced quantum adsorption of neutral atoms in dielectric surfaces

We propose an optical technique to load neutral atoms in quantum adsorption states of a dielectric surface. Considering a realistic atom–surface potential well, we show that free cold lithium atoms approaching a LiF surface may be transferred to a surface bound state of the first excited atomic state. We also discuss schemes to populate adsorption energy levels of the atomic electronic ground state, and we find that spontaneous mechanisms transfer more than 90% of the excited adsorbed atoms into vibrational levels of the fundamental adsorption potential. The lifetime of the resulting two-dimensional waveguide is calculated, considering the adatoms’ interaction with the crystal phonons. PACS 34.50.Dy; 68.43.-h; 68.35.Ja; 32.80.Pj     

Quantum Theory of Surface Polaritons in Semi-Infinite Dielectric Systems

The interaction system of a semi-infinite diatomic dielectric and the electromagnetic field propagating parallelly to the surface is studied. The long-wave optical phonon modes of the semi-infinite dielectric are calculated including the electronic polarizability by a quantum-mechanical theory. Retardation effects are neglected. A quantum field theory method of surface polaritons is developed to calculate the operator describing the interaction between a photon and the phonon polarization fields of the semi-infinite crystal, with explicit inclusion of surface effects. The dispersion relations of the surface phonon-polaritons are derived and discussed. The results are in good agreement with those obtained by the conventional, macroscopic dielectric theory of surface polaritons and experimental ATR (attenuated total reflection) spectra. The dispersion cuwes of polariton leaking modes caused by the interaction between bulk TO mode with surface effect and photons are presented in a graphical form. The k_||-dependence of the electric field strength in each polariton branch is calculated and presented also in a graphical form. We also research the spatial dependence of the field strength in each polariton branch. It is found that these properties are influenced and modulated by the surface phonons because of the interaction between photons and the surface phonon modes of the semi-infinite dielectric system. Hence the divergent nature (diffraction effect) of light propagating along the fib& and waveguides is restrained. We present a method how to use the boundary conditions in the quantum theory, which will be discussed in detail.     

Refractive index,band gap energy,dielectric constant and polarizability calculations of ferroelectric Ethylenediaminium Tetrachlorozincate crystal

Single crystal of Ethylenediaminium Tetrachlorozincate has been grown by slow evaporation method. The single crystal XRD study confirms the orthorhombic structure of the crystal. The presence of functional group vibrations are ascertained through FTIR and Raman studies. In optical studies, the insulating behaviour of the material is established by Tauc plot. The refractive index and the real dielectric constant of the crystal are calculated. The electronic polarizability in the high frequency optical region is also calculated from the dielectric constant values by using the Clausius–Mossotti equation. The large value of dielectric constant is identified through dielectric studies and it points to the ferroelectric behaviour of the material. Further an experimental study confirms the ferroelectric behaviour of the material. The total polarizability of the crystal owing to the space charge, dipole, ionic and electronic polarizability contributions is obtained experimentally, and it matches well with the theoretically obtained value from Penn analysis. Further, Plasmon energy and Fermi energy of the material are also calculated using Penn analysis.     

Optical phonons of circular wires in porous GaP

The reflection spectra of porous gallium phosphide samples are investigated in the far infrared region of wave numbers (10–700 cm^?1). In addition of the longitudinal and transverse optical phonon modes corresponding to the bulk material, additional vibrational modes are detected. Their number and spectral position are correctly described by a model of a dispersive dielectric medium under the assumption that porous gallium phosphide is formed by crystallites whose shape is close to cylindrical. It is concluded that such vibrational modes are optical phonons confined by the volume of the quantum wire. The experimental optical reflection spectra are used to obtain estimates of the average diameter of nanocrystallites forming the porous GaP layer.     

On the theory of vibronic superradiance

The Dicke superradiance on vibronic transitions of impurity crystals is considered. It is shown that parameters of the superradiance (duration and intensity of the superradiance pulse and delay times) on each vibronic transition depend on the strength of coupling of electronic states with the intramolecular impurity vibration (responsible for the vibronic structure of the optical spectrum in the form of vibrational replicas of the pure electronic line) and on the crystal temperature through the Debye-Waller factor of the lattice vibrations. Theoretical estimates of the ratios of the time delays, as well as of the superradiance pulse intensities for different vibronic transitions well agree with the results of experimental observations of two-color superradiance in the polar dielectric KCl:O ₂ ^? . In addition, the theory describes qualitatively correctly the critical temperature dependence of the superradiance effect.     

Theory of radiative and nonradiative transitions for semiconductor nanocrystals

Existing calculations on the radiative and nonradiative transitions in semiconductor crystallites are reviewed with particular emphasis on indirect band-gap materials like silicon for which the quantum confinement effects are more spectacular. It is shown that the crystallite gaps and radiative recombination rates can be predicted with fair accuracy. Effects related to atomic relaxation in the excited state (Stokes shift) are calculated and it is shown that small enough crystallites lead to self-trapped excitons which provide another source of luminescence, much less dependent on size effects. Nonradiative processes are then examined: intrinsic, due to Auger recombination, and extrinsic, due to dangling bond surface states. Both are found to play an essential role in the interpretation of experimental data. Finally, dielectric screening is studied, justifying the use of a reduced internal dielectric constant and providing an estimate of the Coulomb shift due to charging effects.     

Effect of the δ-shaped quantum well at the one-dimensional lattice boundary on properties of Tamm-type surface electronic states

The Tamm-type surface electronic states at the boundary of the one-dimensional structure with periodically potential profile have been theoretically studied under the condition that the δ-shaped quantum well is at this boundary. The properties of surface electronic states in such a structure have been compared with Tamm electronic states in the absence of a quantum well at the lattice boundary and with electronic states localized near the δ-shaped potential well deep in the lattice. In particular, it has been shown that the existence of the δ-shaped potential well at the lattice boundary facilitates a significant increase in the degree of localization of Tamm-type surface electronic states and makes possible the appearance of these states at arbitrarily small heights of lattice potential barriers.     

金刚石晶格上的对角无序与非对角无序非晶量子点

报道金刚石晶格上对角无序与非对角无序非晶量子点的理论研究，用简单的紧束缚哈密顿量描述模型的电子结构，用ｒｅｃｕｒｓｉｏｎ方法求解哈密顿方程，用边界条件对本征值的影响判断局域化，研究发现，带边为扩展态时，带宽的变化趋势与晶态量子点类似；带边为局域态时，尺寸超过某一临界长度后，带宽不变，但带边态密度随尺寸增大而增大。还研究了非晶量子点的介电函数虚部ε₂（?ω）。与扩展态对应的ε₂（?ω），对尺寸变化较敏感。与局域态对应的ε₂（?ω），当尺寸大于 关键词：     

Growth,optical, mechanical,dielectric and theoretical properties of picolinium maleate NLO single crystal

Nonlinear optical single crystals of picolinium maleate (PM) were grown by slow evaporation method. The grown crystal was subjected to single crystal X-ray diffraction analysis to confirm that the crystal belongs to the monoclinic crystal structure with space group P2₁/c. The optical transmission range of the grown crystal was measured by UV–Vis–NIR region with the lower cut-off wavelength as 330 nm. The optical bandgap is found to be 3.75 eV. Mechanical strength of the grown crystal was analyzed using Vickers microhardness tester. Dielectric constant and dielectric loss of picolinium maleate are measured in the frequency range from 50 Hz to 5 MHz at different temperatures. Further, electronic properties, such as valence electron plasma energy, Penn gap, Fermi energy and electronic polarizability of the grown crystal have been estimated.