Theoretical study of Cs adsorption on GaN(0Â 0Â 0Â 1) surface

► Using density functional theory with a plane-wave ultrasoft pseudopotential method based on first-principles calculations, we have found that the most stable positions of Cs adatoms on (2 × 2)GaN(0 0 0 1) surface are at N-bridge and H3 sites for 1/4 monolayer coverage. ► The change of adsorption energies and the change of work function with coverage from 1/4 to 1 monolayer are analyzed, and the reason for those changes is also analyzed. ► These results provide a theoretical reference for the activation experiment of negative electron affinity GaN optoelectronic cathodes.