无序钠团簇的熔化行为
Melting behavior of large disordered sodium clusters
摘要：
用第一性原理恒能分子动力学模拟方法研究了无序钠团簇Na_N（N = 92和142）的类熔化相变. Na_（142）的原子分布在两个主壳层（表面和内部）中，它们与团簇的质心的径向距离不同。130 K，其特征在于由原子的高壳内流动性，和第二，均匀熔融，在约。270 K，涉及整个团簇体积中所有原子的扩散运动（允许壳内和壳间位移）。相反，Na_92的熔化在很宽的温度区间内逐渐进行，在热或结构熔化指示器中没有任何可见的突然步骤。定义明确的步骤在熔化过渡的发生，然后示出有关的存在的分布在壳中的原子。因此，我们提出了一个必要条件，集群被认为是严格amorphouslike（完全无序），即有没有空间区域的集群的原子密度的局部值是相当大的减少。Na_92是所考虑的两个簇中唯一验证此条件的簇，因此其热行为可以被认为是非晶簇的预期热行为的代表。另一方面，Na_142具有可辨别的原子壳结构，应该被认为只是部分无序。这两个集群的热行为进行了比较，二十面体（完全有序）钠簇的相同大小。
英文摘要：
The melting-like transition in disordered sodium clusters Na_N, with N=92 and 142 is studied by using a first-principles constant-energy molecular dynamics simulation method. Na_142, whose atoms are distributed in two (surface and inner) main shells with different radial distances to the center of mass of the cluster, melts in two steps: the first one, at approx. 130 K, is characterized by a high intrashell mobility of the atoms, and the second, homogeneous melting, at approx. 270 K, involves diffusive motion of all the atoms across the whole cluster volume (both intrashell and intershell displacements are allowed). On the contrary, the melting of Na_92 proceeds gradually over a very wide temperature interval, without any abrupt step visible in the thermal or structural melting indicators. The occurrence of well defined steps in the melting transition is then shown to be related to the existence of a distribution of the atoms in shells. Thereby we propose a necessary condition for a cluster to be considered rigorously amorphouslike (totally disordered), namely that there are no space regions of the cluster where the local value of the atomic density is considerably reduced. Na_92 is the only cluster from the two considered that verifies this condition, so its thermal behavior can be considered as representative of that expected for amorphous clusters. Na_142, on the other hand, has a discernible atomic shell structure and should be considered instead as just partially disordered. The thermal behavior of these two clusters is also compared to that of icosahedral (totally ordered) sodium clusters of the same sizes.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
