Fen（n=2～20）团簇的结构、电子和磁性对大小的依赖

Size dependence of structure,electronic and magnetic properties of Fe_n(n=2-20) clusters

使用紧束缚(TB)多体势和遗传算法(GA),计算了Fen (n=2-20)团簇的基态结构.从优化结构出发,使用自洽的紧束缚3d、4s、4p模型哈密顿,计算了每原子平均磁矩(μ)n和向上与向下自旋电子态密度DOS.对小(n≤6)的团簇,Fen的平衡结构非常类似于惰性气体团簇,与硬球堆积相一致.7～12个原子团簇的结构由二十面体的骨架棗五角环组成.14～19个原子团簇形成六角环形结构.所计算的所有团簇的(μ)n都大于块体值,并随着团簇增大缓慢地非单调性地减小.平均配位数、团簇中局域配位数的分布和spd杂化都是影响电子和磁学特性的重要因素.

The ground-state geometries and the binding energy of Fen（n = 2 -20） clusters have been calculated using a TB many-body potential and a Genetic Algorithm （GA）. Based on the optimized geometry, we have calculated the average magnetic moment per atom μn, the density of up and down spin electronic states with a selfconsistent tight-binding model Hamiltonian considering the 3d, 4s, 4p valence electrons. For small（n≤6） clusters, the equilibrium geometries of Fen clusters are very similar to those found in rare-gas clusters and are consistent with hard sphere packing. Clusters containing 7 - 12 atoms exhibit structures consisting of a pentagonal ring that is the backbone of an icosahedron. The structure of Fe13 is an icosahedron . For n = 14 - 19, the clusters form hexagonal ring structures. The μn all have larger values than the bulk value and decrease slowly and non-monotonously with size up. The average coordination number, the local coordination number distributions in cluster geometry and spd hybridization are significant factors to affect the electronic and magnetic properties.