Ethylene oligomerization on single-site Ga 3+ /SiO 2 was modeled based on a Si 8 O 12 (OH) 8 cluster that was adapted from Ugliengo et al. A Ga 3+ single-site was created by substitution of a Si-OH moiety with a Ga atom. The cluster model can be viewed as a finite portion of the solid silica, with the dangling oxygen atoms passivated by hydrogen atoms. The localized nature of oxides and the Ga 3+ center make the cluster model a credible approximation for assessing surface reactivity. Comparisons between the energies and barrier heights calculated on periodic surfaces and the cluster model were used to validate this assumption. Based on an earlier study, initiation of a Gaethyl site from a bare single site and gaseous ethylene was expected to be facile, and a low barrier Ga-ethyl-centered Cossee-Arlman mechanism has been observed. Such active intermediates could easily form when catalysts are treated with hydrogen or ethylene gas. Thus, here the activated Ga-ethyl site with excess ethylene was treated as the starting reactant for network exploration.