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.