First-principles pseudo-potential calculations within density-functional theory framework are performed in order to study the structural and electronic properties of nickel adsorption and diffusion on a GaN(0 0 0 1)-2 x 2 surface. The adsorption energies and potential energy surfaces are investigated for a Ni adatom on the Ga-terminated (0 0 0 1) surface of GaN. This surface is also used to study the effect of the nickel surface coverage. The results show that the most stable positions of a Ni adatom on GaN(0 0 0 1) are at the H-3 sites and T-4 sites, for low and high Ni coverage respectively. In addition, confirming previous experimental results, we have found that the growth of Ni monolayers on the GaN(0 0 0 1) surface is possible. (C) 2010 Elsevier B.V. All rights reserved.