Charge-Transfer Processes in the Assembly of SinOm Neutral Clusters

The chemical bond formation in oxygen-rich SinOm clusters was investigated by sampling the potential energy surface of the model systems SiO + SiO2 -> Si2O3 and (SiO)(2) + SiO2 -> Si3O4 along a two-dimensional reaction coordinate, by density functional theory calculations. Evidence for crossing between the weakly bound neutral-neutral (SiO)(n) + SiO2 and the highly attractive ion-pair (SiO)(n) + SiO2 surfaces was found. Analysis of frontier molecular orbitals and charge distribution showed that surface crossing involves transfer of valence electron charge from (SiO)(2) to SiO2. The sum of the natural atomic charges over the (SiO)(n) and (SiO2) groups of the SinOm cluster products, gave a net positive charge on the (SiO)(n) "core'' and a net negative charge on the (SiO2) groups. This is interpreted as the "ion-pair memory'' left on the SinOm products by the charge-transfer mechanism and may provide a way to assess the role of charge-transfer processes in the assembly of larger SinOm neutral clusters. (C) 2011 Wiley Periodicals, Inc. J Comput Chem 32: 3497-3504, 2011