The energetics and electronic structure of H and a H-H pair in the BCC grain boundary (GB) of Fe have been studied by ASED-MO cluster calculation. The total energy of the cluster decreases when the H atoms are at the GB making it a possible site for H accumulation. Some Fe-Fe bonds in the GB plane shows a 60% decrease in the overlap population when H is present. H-H interaction was also analyzed.

S and H impurities in GB were also studied. The results show that impurities induce large relaxation in the GB and that the GB gives rise to an energetically favorable zone for the H and S accumulation. No S-H association is found and the deleterious effect of H is of much less important when compared with S.