The adsorption of N-2 at the edge of a single-wall carbon nanotube (SWNT) has been investigated employing an ONIOM approach. It was found that N-2 can be chemisorbed at the edge site of zigzag SWNT surface and the N-N bond is activated. However, the adsorption at the edge site of armchair SWNT surface is rather weak. This can be attributed to the crucial effect of local edge carbon atoms arrangement of the defect SWNT surface with open tips. Furthermore, our results strongly reinforce the viewpoint from recent experimental observations and theoretical studies that SWNTs with open tips exhibit larger adsorption capacity than closed-ended SWNTs. (c) 2005 Elsevier B.V. All rights reserved.