Energy barriers for trimethylaluminum (TMA) reaction with varying surface hydroxyl (-OH) density were investigated using density functional theory. When the surface -OH density increased from 0 to 6.8/nm(2) on Si (0 0 1) surfaces, the energy barrier for TMA reaction with the surfaces decreased due to attractive interactions between TMA and -OH. When the surface -OH density further increased to 9.2/nm(2) on a-SiO2 (0 0 1) surfaces, however, the trend was reversed. This was because the attractive interactions between TMA and -OH were decreased due to the attractive interactions of -OH's themselves via hydrogen bond at this high surface -OH density. (C) 2011 Elsevier B.V. All rights reserved.