多体展开势能函数在碳族元素原子簇研究中的应用 Ⅲ.锗原子簇的结构和相对稳定性

Application of the Many-Body Expansion Potential Energy Functions to the Study of Group Ⅳ Atomic Microclusters HI. Structures and Stabilities of Germanium Microclusters

基于从晶体锗确立的多体展开势能函数,本文通过坐标完全优化,发现小的锗原子簇分子(Ge_2—Ge_(14))倾向于形成密堆积结构,表面原子分布以蝶形四元环(D_(2d))为主;常见立方晶体“微观晶体碎片”的分层优化结果表明,在Ge_(15)～Ge_(100)范围内,多数壳层的原子到分子中心的距离均受到压缩,且以畸变的简单立方、面心立方及体心立方较为稳定;在这些畸变密堆积结构中,表面原子向内压缩最为严重,使整个分子趋于球形化.较为开放的金刚石类层状原子簇只有当所含原子数达数百以上时才可能相对更为稳定.

A many-body expansion potential energy function parameterised to the properties of solid germanium is used to study the structures and stabilities of germanium microclusters. Close-packed structures are found for small clusters (Ge2- Ge14), consisting of exclusively four-mem-bered butterfly rings. Shell optimization of the common cubic structures (diamond, sc, bcc, and fcc) indicates that the distorted sc, fcc, and bcc shell clusters with the out-most shells compressed most severely are more stable than diamond-type shell clusters and that diamond structures become more stable only for the clusters containing several hundreds of atoms.