高温下季戊四醇晶体的结构和振动性质的分子动力学模拟(英文)

通过分子动力学研究了季戊四醇晶体在温度高达500K范围内的结构和振动性质.考察了季戊四醇晶体的晶格参数和分子构型等随温度变化情况,相对晶格常数a来说,晶格常数c容易被压缩.发现C-C,C-H和C-O键随温度的变化较大,这意味着在分解过程中这些键可能较敏感,即最先断裂可能性较大.研究了季戊四醇晶体在不同温度下的振动,发现大部分频率随温度的升高而降低.     

钨酸铅晶体的低温红外反射谱

分别在77K、100K、200K和300K温度下测量了钨酸铅(PbWO4,PWO)晶体的红外反射谱,观察到8个反射峰;实验表明PWO晶体在低温77～300K范围内结构稳定.利用Kramers-Kronig(K-K)关系对样品的红外反射谱进行数据处理,获得了不同温度下各振动模的横光学(TO)声子频率ωTO,从而得到了PWO晶体各振动模的温度变化特性,研究表明:Pb2+离子的平动模频率随温度降低发生蓝移,主要是晶格的热膨胀影响;WO42-离子团的振动模频率随温度降低发生红移,主要是非简谐耦合作用影响.     

β-胡萝卜素分子的黄琨因子的温度特性

β-胡萝卜素具有光采集、光防护功能, 又是重要的光电材料, 它在外场下的分子结构和性能变化既有理论意义也有应用价值。测量了β-胡萝卜素在环己醇中68～26 ℃温度范围内的紫外-可见吸收、拉曼光谱。实验结果表明随着温度的降低, 黄琨因子和碳碳键每个振动模的电子-声子耦合常数减小, 紫外-可见吸收光谱红移, 碳碳键拉曼散射截面增加。用线性链状多烯分子的“相干弱阻尼电子-晶格振动模型”、“有效共轭长度模型”等理论给予了解释。随着温度的降低,β-胡萝卜素分子的热无序减小,分子结构有序性增加,π电子离域扩展,有效共轭长度增加,导致紫外-可见吸收光谱红移和强的拉曼活性。相干弱阻尼电子-晶格振动增强,使碳碳键拉曼散射截面增加。引用带有量纲的电子-声子相互作用常数,既可以与黄昆因子建立关系式,计算出碳碳键每个振动模的数值,也可以表征分子的有效共轭长度,π电子离域程度及拉曼散射截面的大小等。     

立方面心C60晶体晶格振动的研究

采用C60 分子之间相互作用势的Kihara形式 ,研究了立方面心C60 晶体的晶格振动问题 ,得到了质心振动沿 [111]、[110 ]及 [10 0 ]方向的声子散射圆频率分布曲线及C60 晶格振动频率的态密度分布 .采用所得到的C60晶格振动频率的态密度分布 ,计算了晶体C60 在 2 98K时的等压热容 ,所得数值与实验值相符 .     

磷酸钠结构的高温拉曼光谱研究

用高温拉曼光谱仪测定了固态和熔融态磷酸钠(Na3PO4)晶体的光谱,分析了磷酸钠晶体的结构及其随温度的变化。通过对从常温谱到高温谱的解析,得出主峰波数随温度的变化及主峰半高宽的变化,可以观察到在600 K附近及1773 K有两个相变产生。此外,磷酸钠晶体的相关高温DSC检测分析,也和拉曼谱中发现的两个相变符合。量子化学理论计算同时对该体系的P-O键振动和平均键长进行了模拟,随着键长的增加,对应的振动频率会降低。还确认了磷酸钠Raman光谱中各个峰的归属,938 cm-1波数处的峰属于(PO4)3-中P-O键的对称伸缩振动,是Na3PO4的特征峰,425及580 cm-1处峰属于磷氧四面体的弯曲振动。     

黄方程与极化激元

如果晶体元胞含两个原子,其格波(具有波的形式的晶格振动模)除了三支声学波外,还有三支光学振动波.在长波极限下(即光学声子波长远大于晶格常数),元胞中两个粒子的光学振动方向相反,而元胞的质心则保持静止.在考虑极性晶体与红外光的相互作用以及电子与晶格的相互作用时,长波长光学振动具有特殊的重要性. 对于极性晶体,正负离子在光学振动时会伴随产生极化,由此产生的宏观电场反过来又影响晶格光学振动模的频率,造成了纵光学振动(振动方向与波传播方向平行)与横光学振动(振动方向垂直于波传播方向)频率的不同.30—40年代的深入研究表明,这种…     

二苯甲酮晶体的红外反射光谱研究

室温下记录了有机非线性光学晶体二苯甲酮三种不同偏振的红外反射光谱（２００－４０００ｃｍ＾－１）。利用Ｋ－Ｋ变换确定了晶格振动模的模，纵频率。根据由Ｋ－Ｋ变换得到的介电常数和折射率的色散曲线外推得到晶体的静态介电常数，高频介电常数和近红外波段的折射率。还对反射带进行了认定。研究表明该晶体二苯甲酮分子间不存在氩键，只以弱的范德华键相结合。结合晶体结构对强反射带出现的原因作了解释。     

温度对马氏体和铁素体晶格常数影响规律

采用同步辐射技术研究了温度对马氏体和铁素体晶格常数的影响规律.研究结果表明,马氏体和铁素体的晶格常数均随着温度的升高而逐渐增大,但马氏体的衍射峰有分峰现象,而铁素体的衍射峰没有分峰现象.对马氏体的{110}和{200}衍射峰进行分峰处理,得到马氏体晶格常数a和c随温度升高逐渐增大,但晶格常数a的增大速度要大于c的速度,即马氏体的正方度逐渐降低.当温度升至500℃时,马氏体正方度c/a=1.铁素体的晶格常数随温度的变化规律与马氏体晶格常数a的基本相同,而与马氏体晶格常数c的明显不同,表明了温度对马氏体晶格常数的影响本质.除此以外,通过对同步辐射数据的分析,建立了马氏体和铁素体晶格常数随温度变化的数值方程.     

不同晶格常数光子晶体构成的光量子阱中的共振模

用基于平面波的传输矩阵法分析由具有不同晶格常数的光子晶体材料构成的光量子阱结构中的共振模，发现湮没于垒层的阱层能带分离成共振模，且共振模的数目随阱层的厚度变化而改变。提出一种新型的非对称量子阱结构模型，由2块晶格常数不同的光子晶体材料和夹在光子晶体材料中间作为阱层的均匀介电材料构成，并对其中的共振模进行了分析。指出当阱层厚度达到构成垒层的光子晶体晶格常数的一半时出现一个共振模，若继续小量增加阱层厚度将使共振模频率出现红移。最后给出一种基于平面波的传输矩阵法，且对于不同晶格常数的光子晶体量子阱结构均有效的数值模拟方法，可用于研究由三维光子晶体材料或者色散材料组成的光子晶体量子阱结构。     

表面极化子光学声子平均数的磁场和温度依赖性

采用变分法、幺正变换和拉格朗日乘子法,研究了有限温度下纯二维晶体中表面磁极化子的性质.讨论了表面光学声子平均数、磁极化子振动频率λ与磁场B、温度T及Lsgrange乘子u之间的关系.对KCl晶体进行了数值计算,结果表明:磁极化子振动频率、表面光学声子平均数均随磁场B的增强而增加,且随温度T升高而增加.当bgrange乘子u超出慢电子范围时磁极化子振动频率、表面光学声子平均数均随u增加而增大且变化越来越显著.     

Pressure effect of structural and vibrational properties of solid pentaerythritol by molecular dynamics simulations

The molecular dynamics simulations (MD) are used to calculate the structural, vibrational and thermodynamic properties of pentaerythritol (PE) crystal up to 4 GPa. The pressure effect for the cell volume, lattice constants, and molecular geometry of solid PE are presented and discussed. It is observed that the C–C bonds has maximum variation, followed by C–H and C–O bonds, which means decomposition of the initial explosion may begin with the C–C bonds. The vibrational frequencies at ambient conditions slightly more than experimental results, and the pressure-induced frequency shifts of these modes are discussed.     

Debye-Scherrer diffraction in the backscattering geometry at the Kurchatov Synchrotron Radiation source. Part 1. Characterization of the method

A technique for Debye-Scherrer diffraction in the backscattering geometry is developed at the Kurchatov Synchrotron Radiation source. It is shown that the sensitivity of the method to a relative change in the lattice constant is higher by two orders of magnitude than that in the forward-scattering geometry. The requirements for experimental apparatus are discussed.     

First-Principles Calculations of Structures and Electronic Properties of Solid Pentaerythritol under Pressure

Structures and electronic properties of the pentaerythritol （PE） crystal under volume compression up to 0.85V0 are studied by E - V fitting method using density functional theory （DFT）. The compression dependences of the cell volumes, lattice constants, and molecular geometries of solid PE are presented and discussed. It is found that the solid PE presents anisotropy along a- and c-axes, and the c axis is the most compressible. Decreasing anisotropy ratio （c/a） with elevating compression suggests an enhancement of the vdW interaction with increasing compression. The C-C and C-H bonds are significantly reduced under compression, which may be related to the sensitivity. The solid PE has indirect band gap （X - G） in the range of the researched compression and the band gap is decreased with compression.     

用力定理计算hcp-WC的基态性质

本文用Kohn-Sham局域密度泛函理论与力定理,在线性丸盒轨道原子球(LMTO-ASA)近似下,计算了hcp-WC的基态性质,包括平衡晶格常数a,体模量B和纵声波速率v。计算结果与实验值对比表明,晶格常数的误差小于10％,讨论了原子球半径比δ的不同选择方案对计算结果的影响。由电子分波压力随晶格常数的变化,分析了hcp-WC的键合特性。 关键词：     

Description of force surfaces in atomic force microscopy with allowance for the mobility of the lattice atoms

The surfaces of constant force and the profiles of the horizontal component of the force during scanning of the tip of an atomic force microscope above the surface of a close-packed lattice in the contact mode are calculated taking account of the mobility of the lattice atoms. It is shown that when the mobility is taken into account, the previously observed discontinuities on the surface of constant force arise at smaller scanning forces on the tip above the surface than in the immobile-atom approximation. The force surfaces arising when scanning above vacancies are obtained. The possibility of using atomic force microscopy data for diagnostics of point defects on a solid surface is discussed.     

非晶(Fe0.99Mo0.01)78Si9B13,Fe78Si9B13合金激波晶化主相α-Fe变化研究

研究激波对非晶FeBSi,FeMoBSi合金的影响,经X射线衍射分析,测定主晶化相α-Fe(Mo,B,Si)晶格常量.结果表明：晶格常量比正常值偏小,用双势模型计算晶格常量,理论值与实验符合得很好.从而肯定晶格常量变小是形成B的替代式固溶体和缺位式固溶体所致. 关键词：     

Modeling of surfaces of constant force above a lattice of close-packed atoms in the repulsive mode

Surfaces of constant force (force contours) are calculated for the scanning of an AFM tip over a lattice of close-packed atoms in the repulsive mode. It is shown that discontinuities are observed on the force contours in the regions between the atoms of the surface lattice for sufficiently small initial scanning heights of a tip with a single atom at its end. A cluster model of the tip end, which ensures continuity of the scanning at arbitrary initial heights, is constructed. The dependence of the AFM images on the orientation of the cluster on the tip end relative to the crystallographic axes of the surface is investigated for both an unperturbed lattice of close-packed atoms and a lattice containing point defects. The diagnostic possibilities of the findings are discussed. Zh. Tekh. Fiz. 67, 77–85 (June 1997)     

Acoustic wave focusing by two-dimensional lattice of cylinders in air

A sound source (3 cm in diameter) image in air, formed in the far wave zone behind a two-dimensional periodic lattice, was experimentally obtained. The lattice consisted of plane parallel rows of steel cylinders with a diameter of 1.58 cm, forming an acoustic crystal with hexagonal structure, The crystal lattice constant (a = 2.14 cm) is smaller than the emission wavelength in air (∼ 3.4 cm). The relations between the emission wavelength and lattice parameters were selected according to model calculation in the second transmission band of the crystal at its negative refractive index n = −0.7. The lateral size of the focused (over the sound pressure distribution) image of the sound source is close to the emission wavelength. A distinctive feature of the experiment is the formation of such a sharply focused image under conditions of an extremely small output aperture (the beam diameter at the acoustic crystal output did not exceed 2.5 acoustic wavelengths in air). It can be considered that the flat acoustic lens is realized. Possible explanations of the observed effect are discussed.     

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