碱金属原子簇的结构和稳定性

基于从体心立方碱金属晶体优化确立的多体展开势能函数，本文通过坐标优化研究了碱金属原子簇Ｘｎ（Ｘ＝Ｌｉ，Ｎａ，Ｋ，Ｒｂ，Ｃｓ）的结构和稳定性。发现：（１）Ｘｎ原子簇（ｎ＝４－２１）倾向于形成畸变四面体结构单元，（Ｔｄ）的密堆积，分子表面被三元环（Ｄ３ｈ）所覆盖，其中Ｘ７－Ｘ１５最优化结构中包含五角双锥Ｘ７（Ｄ５ｈ）结构单元，具有区域五重对称轴；（２）“微观晶体碎片”的分层优化结果表明，体心立方、面心

STRUCTURES AND STABILITIES OF ALKALI METAL CLUSTERS

The structures and stabilitics of alkali metal clusters Xn(X = Li,Na,K,Rb,Cs) were studied based upon the many-body expansion potential energy functions optimized frombody-centered cubic alkali metals.The optimum strictures of small Xn clustcrs(n= 2-21) arefound to be close-packed structures of distorted tetrabcdrons(X4 Td) with molecular surfacescovered exclusively with three-membered rings (X3, D3b).The most stable X7 is a pentagonalbipyramid(D5b)and X7-X15 are derivatives of X7 as strictures of inter-linkcd pentagonalbipyramidal units,suggesting a five-fold local symmetry growth pattern of Xn in the range ofn=7-15.Radially optimized body-centered cubic,face-centered cubic,and hexagonalclose-packed shell-clusters (n= 5-90) are close in binding energies and all much more stablethan diamond and simple cubic shell-clusters.The binding energies pereatom of these clustersincrease slowly and approach the cohesive energies of coresponding bulk metals gradually.