The activation energies for Ga and N desorption from a GaN surface were calculated using the density functional theory to understand the detailed decomposition process of the hydrogen terminated GaN(0 0 0 1) Ga and N surfaces under a hydrogen atmosphere. It was found that the Ga atoms on the hydrogen terminated GaN(0 0 0 1) Ga surface desorbed as GaH molecules from the surface while the N atoms on the hydrogen terminated GaN(0 0 0 1) N surface desorbed as NH3 molecules from the surface. The desorption energies of GaH and NH3 on the hydrogen terminated surface were more consistent with the previous experimental values than those on the ideal surface. These results suggest that the initial surface structure of the GaN(0 0 0 1) surface is terminated with hydrogen. (C) 2009 Elsevier B.V. All rights reserved.