多体展开势能函数在碳族元素原子簇研究中的应用（Ⅳ）──Si_9─Si_（16）原子簇的分子结构与稳定性

Application of the Many-Body Expansion Potential Energy Functions to the Study of Group Ⅳ Atomic Microclusters(Ⅳ)──Structures and Stabilities of Si_9-Si_(16) Microclusters

多体展开势能函数研究表明，Ｓｉ_４－Ｓｉ_（１６）原子簇分子间的结构衍生关系为：依次增加一个二配位或三配位的表面原子，分子表面被四元蝶形环Ｓｉ_４（Ｄ_（２ｄ））所覆盖；Ｓｉ_ｎ（ｎ＝５－１６）结构中多含有Ｓｉ_５（Ｄ_（３ｈ））、Ｓｉ_６（Ｄ_（２ｄ））区域结构单元，笼状Ｓｉ_（１０）及Ｓｉ_（１６）的表面原子均为三配位或三配位以上，预计Ｓｉ_５、Ｓｉ_６、Ｓｉ_（１０）及Ｓｉ_（１６）是硅原子簇碎片化产物分布中丰度较高的序列；在这一范围内的分子结构呈与晶体硅结构（金刚石）无关的密堆积，最高配位数为５，在小于半球的立体角内形成六配位的硅中心，使该簇合物在能量上不稳定。

A many-body expansion potential energy function is used to study the structures and stabilities of silicon microclusters,suggesting that firstly,Si4-Si(16) clusters can be constructed by successively adding two-or three-coordinated atoms,forming surfaces covered with four-membered butterfly rings(D(2d));secondly,the trigonal bipyramid Si5(D(3h)) and D(2d) Si6 are the building blocks for most of these compact structures with a D(4d) cage Si(10) added in for the clusters with over 10 atoms and both Si(10) and Si(16) are covered with three-or four-or five-coordinated atoms,predicting that Si5,Si6,Si(10),and Si(16) be the prominent peaks in the mass spectra of fragmentized silicon clusters,in agreement with experiments;and finally,these nondiamond compact structures have a maximum coordination number of five and the formation of six-coordinated silicon centres within half a sphere leads to destablization in energy.