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.