A complete list of Ga-hydroxyl distance of the 20 tested sites is included in the Supporting Information. We emphasize that the 3CN and 4CN sites, described above, bound the range of the calculated Ga-hydroxyl distances in all considered configurations. We also note that, in our experimental results, XAS on Ga/SiO2 indicates that the majority of sites are Ga 3+ , containing four Ga-O bonds, consistent with the 4CN site model. However, because XAS is a bulk technique, the possible formation of a small amount of 3CN Ga 3+ sites (<10%) cannot be excluded, and exploration of the catalytic relevance of these possible minority sites is a further motivation for the inclusion of the 3CN Ga sites in our analysis.