共查询到20条相似文献,搜索用时 109 毫秒
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精确原子间相互作用势函数的建立是分子动力学模拟的核心. 针对α-B晶体(R3m群), 分别构建Lennard-Jones (L-J)型对势和对势型多体势, 这两类势函数的构建仅需考虑晶体的原子平均结合能和几何构型参数. 前者取最近邻原子间距的势函数为最小值; 后者采用负指数(L-J型)函数和分段插值多项式形式来分别构造势函数, 在近邻处为势能极小值, 相邻极小值位置的中点引入势垒. 针对完整的α-B 晶体和偏离完整α-B晶体结构, 首先利用第一性原理计算结果来确定势函数的参数, 然后借助分子动力学的能量最小化方法优化结构, 并对这两类势函数以及Tersoff 势函数进行比较. 结果表明: L-J对势和Tersoff势的结果与α-B晶体构型有较大偏离; 而对势型多体势, 无论初始晶体构型完整与否, 其结果与完整α-B晶体构型比较一致. 相似文献
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采用分子动力学方法和嵌入原子法(EAM)多体势函数,模拟研究了银纳米团簇在不同温度直到熔化过程中的结构变化,得到了体系能量和热容量随温度的变化关系.结果显示:银纳米团簇在临近熔点附近出现了负热容现象.研究了弛豫后银纳米团簇的稳态结构变化及其在不同时刻结构的演变过程.结果表明:产生负热容现象的主要原因是纳米团簇在熔点附近,结构发生了巨大的变化,形成由{111}和{100}面围成的结构十分稳定和能量更低的多面体. 相似文献
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采用氧化和析出的方法在氧化硅中凝聚生成锗纳米晶体量子点结构. 其形成的锗晶体团簇没有突出的棱角和支晶结构,锗晶体团簇的轮廓较圆混,故可以用球形量子点模型来模拟实际的锗晶体团簇. 对比了在长时间退火氧化条件下和在短时间退火用激光照射氧化条件下所生成的锗纳米晶体结构的PL光谱和对应的锗纳米晶体团簇的尺寸分布. 短时间退火氧化条件下生成的锗纳米晶体较小(3.28—3.96nm),长时间退火用激光照射氧化条件下所生成的锗纳米晶体较大(3.72—4.98nm);其分布结构显示某些尺寸的锗纳米晶体团簇较稳定,适当的氧化条件可以得到尺寸分布范围较窄的锗纳米晶体团簇. 用量子点受限模型计算了锗纳米晶体团簇的能隙结构,用Monte Carlo方法模拟了PL光谱和对应的锗纳米晶体团簇的尺寸分布,分别与实验结果符合较好.
关键词:
锗晶体团簇
纳米晶体
量子点
激光照射 相似文献
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采用分子动力学方法和Quantum Sutton-Chen(QS-C)多体势,对液态金属铜(Cu)凝固过程中的晶体生长规律及纳米团簇微观结构转变特性进行了模拟跟踪研究.运用Honeycutt-Andersen(HA)键型指数法和新的原子团类型指数法(CTIM-2)分析了金属Cu原子的成键类型和原子团簇结构演变特性.结果发现:当以1.0×1013K/s速率凝固时,系统最终形成晶体和非晶体混合共存结构;在以4.0×1012K/s速度冷却时,系统从673K就开始结晶,并形成以1421和1422二种键型为主的晶体结构;面心立方(FCC)和六角密集(HCP)结构在形成晶体铜时起着非常重要的作用,尤其是由1421键型构成的面心立方(12 0 0 0 12 0)基本原子团在晶体生长和纳米团簇结构形成过程中占主导地位. 相似文献
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Density of low-temperature eutectic in magnesium-lead system (83.06 at. % Pb) has been measured by gamma-raying of the samples
with narrow beam from cesium-137 isotope over the temperature range 293–1000 K of solid and liquid states. Approximation density
dependences have been obtained and data of this work and other authors have been compared. Reference tables of temperature
dependences of the alloy thermal properties have been compiled for the entire range of measurements and their errors estimated.
It is shown that differences in the values of volumetric changes obtained during melting and crystallization are bound with
the metastable β′-phase formation. 相似文献
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Two-dimensional Wigner microclusters in a semiconductor dot are studied. Their melting is investigated in detail and it is
shown that, for typical mesoscopic clusters possessing a shell structure, melting occurs in two stages: orientational melting
(rotation of the shells relative to one another) and total melting, where the shells start to overlap with one another and
exchange particles. An example of a “magic” microstructure which has a triangular structure and melts in a single stage is
presented. For this, the temperature dependences of various quantities characterizing cluster structure are investigated.
The change in the distribution of cluster configurations over local minima of the potential energy with increasing temperature
is investigated. At temperatures below the temperature of total melting, a cluster is always located near the configuration
of a global minimum and, at temperatures above the temperature of complete melting, a cluster can be located with finite probability
near configurations corresponding to various local minima of the potential energy.
Fiz. Tverd. Tela (St. Petersburg) 41, 1499–1504 (August 1999) 相似文献
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Mean-field treatments of Yang-Mills theory face the problem of how to treat the Gauss law constraint. In this paper we try to face this problem by studying the excited states instead of the ground state. For this purpose we extend the operator approach to the Random Phase Approximation (RPA) well-known from nuclear physics and recently also employed in pion physics to general bosonic theories with a standard kinetic term. We focus especially on conservation laws, and how they are translated from the full to the approximated theories, demonstrate that the operator approach has the same spectrum as the RPA derived from the time-dependent variational principle, and give—for Yang-Mills theory—a discussion of the moment of inertia connected to the energy contribution of the zero modes to the RPA ground state energy. We also indicate a line of thought that might be useful to improve the results of the Random Phase Approximation. 相似文献
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纳米团簇熔化过程的分子动力学模拟 总被引:3,自引:2,他引:1
本文采用分子动力学结合嵌入原子多体势,模拟了不同半径的Ni纳米团簇的升温熔化过程,研究团簇尺寸对熔点和表面能的影响.模拟结果表明:团簇的熔点显著低于体材料的熔点.团簇熔化的过程首先是在团簇的表面出现预熔,然后向团簇内部扩展,直到整个团簇完全熔为液态.在模拟的纳米尺度范围内,团簇的熔点与团簇尺寸基本成线性关系.团簇的表面能随着团簇尺寸的增大而减小,而且表面能均高于体材料的表面能. 相似文献
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In our previous paper [1], we used the well-known CA(Condensation Approximation) method, to evaluate the adsorption energy distribution from experimental isotherms, assuming that adsorption sites of different adsorption energies are distributed on adsorbent surface completely at randon.This note is an extension of our theory, using the ACCA, (Asymptotically Correct Condensation Approximation), which, in the hitherto investigation, was used only to adsorption on surfaces, with the patchwise topographical distribution of adsorption sites. 相似文献
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通过分子动力学方法模拟了在碳纳米管内填充一定数目的半导体元素硅形成碳纳米管-硅纳米线复合结构的过程,并采用Lindemann指数研究了这种复合结构的热稳定性.计算结果表明,当考虑碳纳米管和硅纳米线轴向方向的周期性边界条件之后,在C(13,0)和C (14,0)碳纳米管内能够形成亚稳结构的硅纳米线Si16NW和Si20NW,从而获得一种碳纳米管-硅纳米线的新型复合结构.通过计算这种复合结构的Lindemann指数,可以看到由于碳纳米管的保护作用,碳纳米管包裹的硅纳
关键词:
复合结构
纳米线
碳纳米管
分子动力学 相似文献
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The thermal conductivity λ and the thermal diffusivity a of liquid rubidium were measured by the laser flash method in the temperature interval from the melting point up to 873 K. The measurement error was 4–6%. The data of this paper were compared with the results of other authors. Approximation equations and the table of reference values for the temperature dependence of λ and a have been obtained. The dependence of the Lorentz number on temperature has been calculated. 相似文献
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A list of 143 binary Laves phases with their melting temperature and melting type is collected, and used to study a correlation between melting temperature and cohesive energy. It is found that the melting temperature of Laves phases is roughly proportional to its cohesive energy calculated by Miedema's empirical model from their intrinsic atomic properties. The average predicted error of melting temperature of compounds is as low as 8.0%. This empirical rule is consistent with the result of the universal binding energy theory of solids. 相似文献
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A mathematical model is developed to describe the melting of nanowires. The first section of the paper deals with a standard theoretical situation, where the wire melts due to a fixed boundary temperature. This analysis allows us to compare with existing results for the phase change of nanospheres. The equivalent solidification problem is also examined. This shows that solidification is a faster process than melting; this is because the energy transfer occurs primarily through the solid rather than the liquid which is a poorer conductor of heat. This effect competes with the energy required to create new solid surface which acts to slow down the process, but overall conduction dominates. In the second section, we consider a more physically realistic boundary condition, where the phase change occurs due to a heat flux from surrounding material. This removes the singularity in initial melt velocity predicted in previous models of nanoparticle melting. It is shown that even with the highest possible flux the melting time is significantly slower than with a fixed boundary temperature condition. 相似文献
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G. A. Rozman 《Physics of the Solid State》2004,46(2):247-248
The thermodynamic properties of alkali halide crystals are considered. Correlations between the thermodynamic characteristics (such as the melting temperature, the melting energy, and the jump in the entropy upon melting) and the binding energy of dipolons are established for 16 alkali halide crystals. 相似文献