The desulfurization of thiophene on a Ni(100) surface has been studied using ab initio local-density-functional calculations. The calculations were performed using the Vienna ab initio simulation package (VASP), which is based on a plane wave basis set and PAW potentials. Starting from preadsorbed thiophene on the nickel surface several reaction pathways for the desulfurization of the thiophene molecule mechanism have been investigated: In the optimized reaction path an energetic barrier of 0.71 eV has been found for this reaction step. In addition the influence of a hydrogenation of the molecule after the initial C-S bond cleavage was investigated. Although the hydrogenation is predicted to lower the barrier for the clesulfurization to 0.14 eV, the barrier for the hydrogenation itself, 0.98 eV, disfavors this process. A detailed analysis of the structural and electronic properties of the molecule in the corresponding transition states is presented. (C) 2003 Elsevier Science (USA). All rights reserved.