Ab initio structures and energetics of selected hydrogenated silicon clusters containing six to ten silicon atoms

The structures and energies of eight fully saturated polycyclic polysilanes (Si6H8, Si6H10, Si7H8, Si7H10, Si8H12, Si9H14, Si10H14, and Si10H16) were investigated using ab initio molecular orbital calculations. Structures and vibrational frequencies were computed at the HF/3-21G(d) level. A complete basis set extrapolation method (CBS-4) was used to calculate the energies of the structures. Heats of formation were evaluated based on homodesmotic reactions involving disilane, trisilane, and isotetrasilane. The calculations predict a negative free energy of reaction for cluster formation from silane (with H2 as a by-product) for conditions typically used in chemical vapor deposition of silicon from silane.