The　magnetic　interactions　in　Ni-doped　ZnO　are　calculated　using　GGA　and　GGA　+　U　method　of　density　functional　theory.　The　following　three　cases:　(i)　Ni-doped　ZnO,　(ii)　(Ni,　Al)-codoped　ZnO,　and　(iii)　(Ni,　Li)-codoped　ZnO　are　studied.　The　ferromagnetic　ordering　is　always　favorable　for　the　three　cases　within　GGA　method.　However,　the　ferromagnetic　state　is　sometimes　favorable　after　treating　within　the　method　of　GGA　+　U.　The　GGA　underestimates　the　correlated　interactions　especially　when　the　Ni　ions　align　directly　to　each　other.　(C)　2007　Elsevier　B.V.　All　rights　reserved.