The structures and properties of FeSin/FeSin+/FeSin- (n=1∼8) clusters

The geometry, stability, and electronic properties of iron-doped silicon clusters FeSin/FeSin+/FeSin- (n = 1 similar to 8) have been systematically investigated using the density functional theory (DFT) approach at the B3LYP/6-311+G* level. Our results show that the ground state structures FeSin/FeSin+/FeSin- change from planar to three-dimensional for n > 3. Bipyramidal structures, or their face-capped isomers, are favored for the larger clusters. For neutral FeSin clusters, their ground state structures are the trigonal, tetragonal, capped tetragonal, capped pentagonal, and combined tetragonal bipyramids for n = 4 similar to 8, respectively. The lowest-energy structures of the anionic FeSin- clusters essentially retain similar frameworks to their neutral counterparts, while those of the cationic FeSin+ clusters are significantly deformed; this is confirmed by their calculated ionization potential and electronic affinity values. For most of the stable structures, the spin electronic configurations are s = 1 or 2 for neutral FeSin, s = 3/2 or 5/2 for ionic FeSin+/FeSin-. The average binding energy values generally increase with increasing cluster size, indicating the clusters can continue to gain energy during the growth process. Fragmentation and second-order energy peaks (maxima) are found at n = 2, 5, and 7 for FeSin/FeSin-, n = 4 and 6 for FeSin+, suggesting that these clusters possess higher relative stability. Furthermore, the HOMO-LUMO gap values show that anionic FeSin- have greater chemical reactivity than cationic FeSin+ and neutral FeSin, except when n = 7.