Employing　density　functional　theory　(DFT),　the　adsorption　and　dehydrogenation　mechanism　of　ammonia　on　clean　and　O-covered　Cu　(111)　surfaces　have　been　studied　systematically.　Different　adsorption　geometries　were　investigated　for　NH3　and　related　intermediates.　In　addition,　the　stable　co-adsorption　configurations　for　the　relevant　co-adsorption　groups　were　identified.　The　projected　density　of　states　(DOS)　were　calculated　to　understand　the　interaction　between　NHx　(x　=　1,　3)　species　and　Cu　(111)　surface　and　investigate　the　effect　of　oxygen　atom　on　adsorption.　Finally,　transition　states,　energy　barriers　and　reaction　energies　were　determined　to　confirm　the　mechanism　of　dehydrogenation　of　NH3　on　clean　and　oxygen-covered　Cu　(111)　surfaces.　It　was　shown　that　NH　is　the　most　abundant　intermediate　on　clean　and　O-covered　Cu　(111)　surface　due　to　the　highest　energy　barrier,　suggesting　the　dehydrogenation　of　NH　group　is　the　rate-determining　step　in　the　overall　reaction.　Furthermore,　the　existence　of　oxygen　atom　can　reduce　the　energy　barriers　drastically　and　promote　the　decomposition　of　NHx　(x　=　1-3),　indicating　that　ammonia　decomposition　is　more　favorable　on　oxygen-covered　Cu　(111)　surface.　(C)　2014　Elsevier　B.V.　All　rights　reserved.