First-principles Calculations of H2O Adsorption Reaction on the GaN（0001） Surface

The adsorption and decomposition of H2O on GaN(0001) surface have been explo-red employing density functional theory (DFT). Two distinct adsorption features of H2O on GaN(0001) corresponding to molecular adsorption and H-OH dissociative adsorption are revealed by our calculations. The activities of the surface reactions of H2O on GaN(0001) surface are investigated. For the stepwise processes of H2O decomposition into H2 in gas phase and adsorbed O atom (H2O(g) → H2O(chem)→ OH(chem) + H(chem)→ 2H(chem) + O(chem)→ H2(g) + O(chem)), the first and second steps are facile and can even occur at room temperature; while the last two have high barriers and thus are difficult to proceed, especially the fourth step is endothermic. In short, H2O adsorption and decomposition into H2 in gas phase and adsorbed O atom on GaN(0001) surface are exothermic by -43.98 kcal/mol.