Effect of hydrogen on ground state properties of silicon clusters (SinHm;: n=11-15, m=0-4):: a density functional based tight binding study

The effect of hydrogen addition to silicon clusters Si-n (n = 11-15) is examined in terms of the change in their ground state geometry, bonding characteristics ( bond lengths, bond angles and Si coordination numbers), structural stability, vibrational spectra and electronic structure. We found that addition of hydrogen caused a drastic change in the structural geometry of silicon clusters. Upon hydrogenation, some clusters become highly symmetric, while some others are completely distorted. Hydrogenation caused a structural transition in silicon clusters; from spherical to elongated in Si-11 and Si-12, from one side capped elongated to both side capped elongated in Si-13 and Si-14 and from both side capped elongated to one side capped elongated in Si-15. Hydrogen preferred to bond with either under-coordinated or over-coordinated Si atoms. Each H atom is bonded to only one Si atom and localized outside the silicon cluster skeleton. Hydrogenation caused a significant change in the vibrational spectra and electronic structures of bare Si-n silicon clusters. There exists a band gap near the Fermi level in EDOS in all the bare and hydrogenated silicon clusters. The band gap of a silicon cluster depends on its size and amount of hydrogenation.