小金属团簇fission中的几何和统计因素
Geometrical and statistical factors in fission of small metal clusters
摘要：
用密度泛函理论方法，以Na_{10} ^{2+}和Na_{18} ^{2+}团簇为例，研究了亚稳态带电单价金属团簇的裂变.能量的过程，即离解能和裂变势垒，以及它的动力学，即裂变途径，进行了分析。计算了Na_{10} ^{2+}团簇全范围裂变通道的离解能和裂变势垒。阐明了团簇结构对裂变过程的影响。计算结果表明，小碎片的几何形状和它在大碎片中的近邻的几何形状在决定裂变势垒高度方面起着主导作用。本研究表明，在裂变过程中的集群结构的重排的重要性。它可能包括在两个碎片之间形成一个颈部，或者通过母星系团的另一种异构体状态进行裂变;给出了这种过程的例子。计算了Na_{10} ^{2+}团簇的几个低激发态的跃迁势垒，并与相应的裂变势垒进行了比较。这些数据表明，有一个竞争之间的“直接”裂变和裂变通过中间异构态的母集团。团簇的几何形状对系统的熵的变化，由于裂变的影响进行了讨论。
英文摘要：
Fission of metastable charged univalent metal clusters has been studied on example of Na_{10}^{2+} and Na_{18}^{2+} clusters by means of density functional theory methods. Energetics of the process, i.e. dissociation energies and fission barriers, as well as its dynamics, i.e. fission pathways, have been analyzed. The dissociation energies and fission barriers have been calculated for the full range of fission channels for the Na_{10}^{2+} cluster. The impact of cluster structure on the fission process has been elucidated. The calculations show that the geometry of the smaller fragment and geometry of its immediate neighborhood in the larger fragment play a leading role in defining the fission barrier height. The present study demonstrates importance of rearrangement of the cluster structure during fission. It may include forming a neck between the two fragments or fissioning via another isomer state of the parent cluster; examples of such processes are given. For several low-lying isomers of Na_{10}^{2+} cluster the potential barriers for transitions between these isomer states are calculated and compared with the corresponding fission barriers. These data suggest that there is a competition between "direct" fission and fission going via intermediate isomer states of the parent cluster. An impact of the cluster geometry on the change of the system's entropy due to fission is also discussed.
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