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 TiSin 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 TiSin clusters favor Si-capped TiSin−1 structures, with the lowest energy structure of TiSi2, TiSi3, TiSi4, TiSi5, TiSi6, TiSi7 and TiSi8 being Si-side-on TiSi adduct, Si-face-capped TiSi2 triangle, Si-face-capped TiSi3 trigonal pyramid, Si-face-capped TiSi4 trigonal bipyramid, Si-face-capped TiSi5 square bipyramid, Si-face-capped TiSi6 pentagonal bipyramid, and Si-face-capped TiSi7 capped pentagonal bipyramid, respectively. The ground state structures obtained herein for the neutral TiSin clusters agree well with those of Guo et al. except for TiSi3 and TiSi8. Adding or removing an electron greatly changes some ground state structures, i.e. for TiSi3 −/TiSi3 +, TiSi5 −, TiSi6 −/TiSi6 + TiSi7 − and TiSi8 −/TiSi8 +; others are almost unchanged, e.g. TiSi2 −/TiSi2 +, TiSi4 −/TiSi4 +, TiSi5 + and TiSi7 +. 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 TiSin/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 TiSi5, anionic TiSi5 − and cationic TiSi6 + are relatively stable.