共查询到19条相似文献,搜索用时 203 毫秒
1.
2.
本文论述价键优选法作为一种新颖的理论方法在材料结构预测与物性研究中的应用, 特别是在低维数纳米结构如团簇与纳米线研究中所展示的优势. 价键优选法以原子几何构型和电子云(主要是由费米能级附近的分子轨道组成, 即广义前线轨道)空间分布来合理决定纳米结构的稳定构型的选取. 本文以硅团簇为例说明价键优选法的特点, 以及锂、钠、铍、镁等金属团簇为例说明价键优选法在结构预测与材料 物性随尺寸演化规律研究中的应用, 以锂离子在MoS纳米线中的吸附为例说明价键优选法在储能材料离子传导研究中的应用, 最后总结价键优选法的进一步发展方向.
关键词:
价键优选法
团簇
纳米结构
离子传导 相似文献
3.
采用密度泛函理论中的广义梯度近似(GGA)对CoBen(n=1—12)团簇的几何构型进行优化,并对能量、频率和磁性进行了计算,同时考虑了电子的自旋多重度.得到了CoBen(n=1—12)团簇最低能量结构的自旋多重度是2和4.在CoBen(n=1—12)团簇中,Co原子的磁矩出现了奇偶振荡,当n=6时,Co原子的4s,3d和Be原子的2s,2p较强杂化、Co-Be键长的减小以及对称性的降低导致Co原子的磁矩最小.通过对CoBen(n=1—12)团簇电子性质的分析,得出了掺杂可以增强团簇稳定性和有利于增加合金化学活性的结论.n=5,10是团簇的幻数.
关键词:
n团簇')" href="#">CoBen团簇
自旋多重度
磁矩
电子性质 相似文献
4.
采用密度泛函理论对CO吸附在镍团簇表面进行了系统研究.结果表明,NinCO团簇的最低能量结构是在Nin团簇最低能量结构的基础上吸附CO生长而成,CO的吸附没有改变Nin团簇的结构;CO分子在Nin团簇表面发生的是非解离性吸附,与优化的CO键长(0.1138?nm)相比,吸附后C—O键长变长(0.1180—0.1214?nm),表明吸附后C—O键被削弱,CO分子被活化.自然键轨道分析表明,CO分子只与最近邻的Ni原子发生相互作用;CO分子与Ni原子相互作用的本质是CO分子内的杂化轨道与Ni原子3d, 4s, 4p轨道相互作用的结果.
关键词:
nCO团簇')" href="#">NinCO团簇
n团簇')" href="#">Nin团簇
平衡结构
电子性质 相似文献
5.
用密度泛函理论(DFT)的杂化密度泛函B3LYP方法在6-31G基组水平上对MgmBn(m=1,2;n=1-4)团簇各种可能的构型进行几何结构优化,预测了各团簇的最稳定结构.并对最稳定结构的振动特性、电离势、成键特性、极化率和超极化率等性质进行了理论研究.结果表明,团簇的最稳定结构大多是平面结构,团簇的稳定结构中通常是几个呈负电性的B原子形成一个负电中心,而其他B原子和Mg原子通常处在端位,且显正电性;团簇中通常是B-B键和B-Mg键共存,极少出现Mg-Mg键,
关键词:
mBn(m=1')" href="#">MgmBn(m=1
n=1-4)团簇
密度泛函理论
结构与性质 相似文献
6.
7.
本文结合CALYPSO软件和密度泛函理论,详细研究了MB80/-(M=Li、Na、Rb、Cs)团簇的几何结构和成键特性.结构分析结果表明,MB80/-团簇的基态结构都具有相似的几何构型,均为七棱锥状结构,并且随着掺杂原子的原子序数的增加,其M-B键的键长呈增加的趋势.通过稳定性分析,我们发现Li B8-团簇的最高占据分子轨道与最低未占据分子轨道之间的能隙(HOMO-LOMO能隙)以及结合能(Eb)最大,因此这个团簇是体系中相对稳定的结构.电荷转移分析表明,掺杂的碱金属原子在所研究体系中充当着电子供体的角色.最后,成键分析的结果显示,Li B8-团簇的稳定性来源于B原子的2p轨道以及Li原子的2s和2p轨道在HOMO和LUMO的高贡献;适应性自然密度划分分析显示,B和Li原子都参与了成键,这同样有利于Li B8-1团簇的高稳定性的形成.希望我们的工作... 相似文献
8.
采用密度泛函(DFT)中的B3LYP方法,选择sto-3g基组,优化并得到了TinMg(n=1—10)小团簇的基态平衡结构,计算出了掺杂团簇的基态结构的平均键长、对称性、原子化能、能级分布、能级间隙、束缚能、总能的二阶差分. 结果表明,随着团簇原子数的增加,镁原子更容易趋于团簇表面位置,镁-钛平均键长大于钛-钛平均键长,以对称性结构为最稳定的基态结构,且呈多个五角双锥结构. 其中Ti5Mg和Ti8Mg的结构更为稳定.
关键词:
密度泛函
钛-镁团簇
基态结构 相似文献
9.
10.
采用分子动力学结合嵌入原子方法对比研究了Co分布于Cu-Co团簇不同层的结构和性质.研究表明:Co原子分层掺杂可对团簇的结构转变点和熔点进行诱导控制;分层掺杂的Cu-Co团簇第一相变是一种扩散度较小的由立方八面体转变为二十面体的相变;Co原子易于向低能态团簇的亚表层(111)面偏析,从而诱导团簇结构紊乱,造成其熔点差异. 相似文献
11.
X.-Y. Shen Y.-G. Xu C.-L. He H.-T. Liu J.-M. Li 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2005,34(1-3):109-112
We present an optimum valence bond scheme to study
important stable geometric structures of clusters, by combining
the characteristics of frontier molecular orbitals and the
first-principle molecular dynamics simulation. It is interesting
to note that even for small size clusters it has already provided
clues in some macroscopic properties of the second- and the third-row elements in the period table (e.g. melting and boiling point). 相似文献
12.
D. Cheng D. Cao 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,66(1):17-23
Canonical ensemble Monte Carlo simulations are applied to investigate the
melting of the icosahedral 55-atom Ag-Cu-Au clusters. The clusters are
modeled by the second-moment approximation of the tight-binding (TB-SMA)
many-body potentials. Results show that the introduction of the only Cu atom
of the third alloying metal in the bimetallic Ag43Au12 cluster,
forming the Ag42Cu1Au12 cluster, can greatly increase the
melting point of the cluster by about 100 K. It is also found that the
substitution of the only Cu atom of the third alloying metal in the
Ag1Au54 clusters, forming the Ag1Cu1Au53 cluster,
can result in an increase of 40 K in the melting point. It can be concluded
that the melting points of the bimetallic clusters can be tuned by the third
metal impurities doping. In addition, the surface segregation of Ag atoms in
the Ag-Cu-Au trimetallic clusters occurs even after melting. 相似文献
13.
基于半经验的Gupta原子间多体相互作用势, 采用分子动力学方法并结合模拟退火及淬火技术, 系统研究了小尺寸铝团簇Aln (n=13–32)的熔化行为. 模拟结果表明: 除个别尺寸(Al13 和Al19) 外, 团簇熔化过程比热曲线普遍呈现杂乱无规(无明显单峰)现象, 这与实验观测小Al团簇比热普遍无规的结果完全一致. 通过分析不同温度点上团簇淬火构型的势能分布图给出了小Al团簇比热呈现无规或有规现象的成因. 对于比热无规团簇, 可以利用原子等价指数判断给出团簇熔点, 所得团簇熔点随团簇尺寸的变化趋势与实验观测结果完全一致.
关键词:
Gupta势
团簇
分子动力学
熔化 相似文献
14.
We find that the potential energy distribution of atoms in clusters can consistently explain many important phenomena related to the phase changes of clusters, such as the nonmonotonic variation of melting temperature with size, the dependence of melting, boiling, and sublimation temperatures on the interatomic potentials, the existence of a surface-melted phase, and the absence of a premelting peak in heat capacity curves. We also find a new type of premelting mechanism in double icosahedral Pd19 clusters, where one of the two internal atoms escapes to the surface at the premelting temperature. 相似文献
15.
J. W. Hewage W. L. Rupika F. G. Amar 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2012,66(11):1-7
Classical molecular dynamics simulation (MD) with Sutton-Chen potential has been used to generate the minimum energy and to study the thermodynamic and dynamic properties of mixed transition metal cluster motifs of Ag n Ni(13?n) for n ?? 13. Literature results of thirteen particle clusters of neat silver and nickel atoms were first reproduced before the successive replacement of the silver atom by nickel. Calculation was repeated for both silver-centred and nickel-centred clusters. It was found that the nickel-centred clusters were more stable than the silver-centred clusters. Heat capacities and hence the melting points of silver and nickel-centred clusters were determined by using the Histogram method. Species-centric order parameters developed by Hewage and Amar were used to understand the dynamic behaviour in the transition of silver-centred clusters to more stable nickel-centred clusters. This species-centric order parameter calculation further confirmed the stability of nickel-centred clusters over those of silver-centred species. 相似文献
16.
应用基于嵌入原子方法的分子动力学计算研究了Cu57和Cu58团簇在升温过程中变为熔体的结构演化过程.两个团簇在熔化时表现出不同的结构变化行为,进而影响到它们能量变化的差异.在升温时,团簇不同区域的原子局域结构变化由原子密度分布函数确定.模拟表明,即使对于这两个仅相差一个原子的小尺寸团簇,结构变化也敏感于团簇的尺寸. 相似文献
17.
18.
利用紧束缚分子动力学方法研究了硅团簇Sin(n=5—10)的熔化行为.给出了团簇 熔化潜热 和熔点随团簇尺寸的变化关系,表明团簇熔化潜热和熔点强烈依赖于团簇的原子数.计算结 果表明硅团簇熔化机理与金属团簇熔化有很大不同,金属小团簇的熔化是一个从低温类固态 向高温类固态转变的过程,在转变温区,类固态和类液态处于动力学共存,而硅团簇在转变 温区则是处于一种中间态,这种中间态既不是类固态又不是类液态.比较了用不同计算方法 和定义方法所得硅团簇熔点.
关键词:
紧束缚
硅团簇
熔化潜热 相似文献
19.
The potential energy surfaces for clusters of some three to sixty atoms under Lennard-Jones forces have been systematically explored using numerical optimization techniques. In searching for minimum-energy configurations three particularly compact non-lattice growth schemes emerge showing tetrahedral, pentagonal (D5 h ) and icosahedral symmetry respectively. All these systems were found to be appreciably more stable than microcrystallites based on the face-centred cubic structure while certain lattice elements were shown to be metastable for small numbers of atoms. Some qualitative conclusions are then drawn concerning the occurrence of saddle-points for delocalized motion and the contribution of these to the generation of configurational entropy in small clusters. A crucial feature of the energy surfaces examined is the breakdown of strict local symmetry in compact clusters of more than two ‘shells’ of atoms and the possibility of delocalized motion of surface atoms around a solid-like core. These and other qualitative thresholds are pointed out as possible manifestations of entropy which could contribute to the existence of a ‘critical nucleus’ for discrete clusters with a role similar to that played in liquid-drop theories. 相似文献