Ab initio study of the polymerisation of cyclopentasilane

The molecular structures and vibration modes of cyclopentasilane (Si₅H₁₀) have been examined by employing ab initio and density-functional methods. Three different structures of Si₅H₁₀ with different symmetries are analysed, and the results show that the envelope (C _s ) and the twist (C₂) forms have similar energies and that the planar form (D_5h ) is about 50 meV less stable than the C _s and C₂ forms. The excited-state potential energy surface of Si₅H₁₀ is performed using the CIS electronic energy calculation. The ring-open reaction of Si₅H₁₀ is investigated in detail by using the first-principles molecular-dynamics simulation for screening the reaction pathways. The formation of Si–H–Si is found to play an important role in the ring-open reaction.