Potential energy surfaces of Si _mO _n cluster formation and isomerization

The reaction paths for formation and isomerization of a set of silica Si _mO _n (m = 2,3, n = 1-5) nanoclusters have been investigated using second-order pertubation theory (MP2) with the 6-31G(d) basis set. The MP2/6-31G(d) calculations have predicted singlet ground states for all clusters excluding Si ₃O ₂. The total energies of the most important points on the potential energy surfaces (PES) have been determined using the completely renormalized (CR) singles and doubles coupled cluster method including perturbative triples, CR-CCSD(T) with the cc-pVTZ basis set. Although transition states have been located for many isomerization reactions, only for Si ₃O ₃ and Si ₃O ₄ have some transition states been found for the formation of a cluster from the separated reactants. In all other cases, the process of formation of Si _mO _n clusters appears to proceed without potential energy barriers.