共查询到18条相似文献,搜索用时 125 毫秒
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用简单数学方法就体心立方晶格和面心立方晶格证明了三维情况下布里渊区体积等于倒格子原胞体积.同时提出证明高阶布里渊区与简约布里渊区体积相等的一种简捷方法. 相似文献
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本文在简谐近似下采用原胞法求解一般情况下的一维双原子链的格波解和色散关系,讨论原子链结构参数对其色散关系的影响以及原胞内原子的振动特点。研究结果表明,晶格常数一定的情况下一维双原子链的色散关系与近邻原子相对间距无关;在布里渊区中心,长声学支格波近似为连续的弹性介质波,而长光学支格波近似为原胞内原子相对振动而原胞质心不动的驻波;在近邻原子间距和恢复力系数均相等的情况下,在布里渊区边界处短声学支格波和短光学支格波分别近似为波节在小原子和大原子的驻波。本文相关内容可为固体物理教学提供优质教学素材。 相似文献
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考虑电子-声子耦合强度因维度而异,导出了描述三维、二维和一维混晶中电子-声子相互作用的哈密顿量。考虑构成三元混晶的两种二元晶体的晶格失配会使混晶体积随元素组分比改变,在推导三维、二维和一维三元混晶中极化子自陷能量和重整化有效质量时计入了离子相对位移与二元晶体原胞体积的关系。结果表明:磷化物三元混晶中极化子自陷能量和重整化有效质量随元素组分的变化关系呈明显的非线性特征,对晶格适配明显、电子-声子耦合较强的材料,体积效应不可忽略。维度越低,非线性特征和体积效应越明显。 相似文献
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本文用正电子湮没技术对超高分子量聚乙烯退火处理后的结构进行了研究。用PATFIT-88软件件分析了正电子湮没谱,给出了在100℃条件下,样品的结晶度。自由体积和自由体积分数随退火的变化。实验证明,结晶度.自由体积和自由体积分数在退火初期变化最快,随着退火时间增加变化趋于平缓。这一结果与Wunderlich提出的理论相一致。 相似文献
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在考虑自由体积和局部临界扩散势能的基础上,提出一种新的计算自扩散系数模型,并给出新模型中各个因子物理含义.同时还提出一种计算局部临界扩散势能的新方法,并应用于新模型.另外将衍生van der Waals状态方程应用于求解自由体积,式中所需径向分布函数由Morsali-Goharshadi方程得到.在相同条件下,新模型比原自由体积模型更准确. 相似文献
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利用第一性原理平面波赝势密度泛函理论, 并结合准谐德拜模型, 计算了立方萤石结构ErH2在不同温度和压强下的体积、热膨胀系数、体弹模量和等体热容等弹性性质及热力学性质。在温度高于1 100 K的条件下,计算出的等体热容趋近于Dulong-Petit极限。得到了绝对零度、零压强下ErH2的该结构的晶格常数为0.523 2 nm,与实验值0.523 0 nm非常接近。由不同的原胞体积得出了该体系的单点能与原胞体积的关系的数据;从计算出的高压下的弹性常数,根据立方晶系的力学稳定性条件,推断出立方萤石结构ErH2的相变压力约为20 GPa。 相似文献
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针对不同教材中关于面心立方晶格和体心立方晶格的第一布里渊区的描述,本文通过对称性作图的方式直观地给出了这两种结构第一布里渊区的确定方法,并通过与空间可能存在的5种正多面体的特征的对比,提出了这两类晶格第一布里渊区的更为合理和统一的命名方法. 相似文献
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《中国光学快报(英文版)》2020,(6)
Rotating elliptical nanowire arrays as two-dimensional photonic crystals has been proposed and studied in this Letter. The analysis of the four lowest energy bands and the first bandgap width of some examples illustrates that the rotation and configuration of the primitive cell can have effects on the reducibility of the Brillouin zone.As the central element's orientation changes, the irreducible Brillouin zone could be expanded to the whole first Brillouin zone. Special attention has been paid to the nanowire arrays with adjacent elements perpendicular to each other, and the irreducible Brillouin zone unexpectedly retracted back to the 1/8 of the first Brillouin zone though the symmetry of elements is lower than that of the square lattice. Meanwhile, the first bandgap width of the perpendicular array can be adjusted by the rotation of each primitive element. 相似文献
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The Raman spectra of an oriented single crystal of β-LiNH4SO4 show that the first order phase transition involves a doubling of the primitive unit cell and is characterized by an unstable pair of degenerate phonons at the Brillouin zone boundary. This pair of phonons couples with the A2 species strain component in the free energy expansion to give a term typical of improper ferroelastics. 相似文献
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The Wigner-Seitz cell of a lattice inn-dimensional space displays the complete point group of such a lattice. The vertices of the cell when projected onto pseudo
space can serve as the outer shape of acceptance domain or motif. This general procedure leads to acceptance domain or motif
identical to those discussed in literature for primitive orthogonal hyperlattices.
Example of 4d non-orthogonal hyperlattices corresponding to 12-fold symmetry will be considered. It will be shown that the
first Wigner-Seitz cell degenerates into more than one shape in 2d pseudo space and can serve as a natural partition of the
motif. Following a parallel procedure, the consequence of projection of first 4d Brillouin zone will also be discussed. 相似文献
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It is shown how one can obtain, extending Birman's method, the symmetry of the soft modes in general second order phase transitions which occurs at points in Brillouin zone accompanying the primitive cell volume enlargement. This method is much simpler than the usual Landau method which utilizes the free energy expansion and its minimization. Gd2(MoO4)3 is taken as an example. The case in which several arms of star-k contribute to the transition is also discussed using the example of C64h→C62h. 相似文献
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A method is proposed for constructing appropriate sets of special points in the Brillouin zone in which the extended unit cell method is used with a subsequent shift from the center of the reduced Brillouin zone. The proposed method offers several advantages over the commonly used Monkhorst-Pack method. The difference in the construction of sets of special points for the direct and reciprocal lattices is discussed for crystals belonging to a nonsymmorphic space group. The cases of a planar square lattice and an fcc lattice are considered to illustrate general results. 相似文献
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Summary A general method to calculate electronic Green’s functions in the tight-binding scheme is presented. The integrations are
systematically reduced to the irreducible volume of the first Brillouin zone, so that a very short time is necessary for the
computer’s work. The importance of symmetry planes, lines and points is stressed.
Riassunto Si presenta un metodo generale per il calcolo delle funzioni di Green elettroniche nell’approssimazione degli elettroni fortemente legati. Le integrazioni sono sistematicamente ridotte al volume irriducibile della prima zona di Brillouin, in modo da ridurre notevolmente il tempo di calcolo. Si mette in risalto l’importanza di piani, linee e punti di simmetria.相似文献
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The dependence of the energy on the quasi-momentum of optical and acoustic phonons in diamond-type crystals is analyzed. It is shown that the dispersion relation of optical branches near the Brillouin zone center in such crystals can be derived based on the modified Klein-Gordon equation corresponding to quasiparticles (optical phonons) with negative effective mass. Analytical expressions are derived for dispersion curves of acoustic and optical branches in the entire Brillouin zone, based on the sinusoidal approximation. The obtained analytical dependences of dispersion relations are compared to the experimental results of the study of inelastic neutron scattering spectra in diamond crystals. The law of the coordinate and time transformation for optical phonons with negative effective rest mass when going to the new inertial reference frame, similar to Lorentz transformations in relativistic mechanics, is determined. 相似文献
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The existence of surface states in band gaps of a nearly free electron band structure is investigated. While in gaps at the Brillouin zone boundary one finds such a state only for positive potential matrix element, there a surface state always exists for band gaps inside the Brillouin zone. 相似文献