Theoretical Studies on the Structures and Stabilities of Charged, Titanium-Doped, Small Silicon Clusters, TiSi_n -~/TiSi_n +~(n = 1-8)

摘要

The structures and stabilities of charged, titanium-doped, small silicon clusters TiSi_n +~/TiSi_n - ~(n = 1-8) have been systematically investigated using the density functional theory method at the B3LYP/6-311+G~* level. For comparison, the geometries of neutral TiSi_n clusters were also optimized at the same level, although most of them have been reported previously (Guo et al., J Chem Phys 126: 234704, 2007). Our results indicate that all neutral TiSi_n clusters favor Si-capped TiSi_n-1 structures, with the lowest energy structure of TiSi_2, TiSi_3, TiSi_4, TiSi_5, TiSi_6, TiSi_7 and TiSi_8 being Si-side-on TiSi_adduct, Si-face-capped TiSi_2 triangle, Si-face-capped TiSi_3 trigonal pyramid, Si-face-capped TiSi_4 trigonal bipyramid, Si-face-capped TiSi_5 square bipyramid, Si-face-capped TiSi_6 pentagonal bipyramid, and Si-face-capped TiSi_7 capped pentagonal bipyramid, respectively. The ground state structures obtained herein for the neutral TiSi_n clusters agree well with those of Guo et al. except for TiSi_3 and TiSi_8. Adding or removing an electron greatly changes some ground state structures, i. e. for TiSi_3~-/TiSi 3~+, TiSi_5~-, TiSi_6~-/TiSi_6~+ TiSi_7~- and TiSi_8~-/TiSi_8~+; others are almost unchanged, e. g. TiSi_2~-/TiSi 2~+, TiSi_4~-/TiSi 4~+, TiSi_5~+ and TiSi_7~+. Based on the optimized geometries, various energetic properties, including binding energies, fragmentation energies, second-order difference energies, HOMO-LUMO energy gaps, ionization potentials and electron affinities, were calculated for all the most stable isomers. The average binding energies reveal that all of TiSi_n/TiSi n +/TiSi n - (n = 1-8) clusters can continue to gain energy as the size increasing. The fragmentation energies and second-order energy differences suggest that neutral TiSi_5, anionic TiSi_5~- and cationic TiSi_6~+ are relatively stable.