The H-Fe interaction at a grain boundary in body-centered cubic Fe was studied by using qualitative electronic structure calculations within the framework of the atom superposition and electron delocalization molecular orbital theory. Calculations were performed by using a Fe196 cluster to simulate the 36.9° [100]{013} symmetrical tilt grain boundary structure. The most stable positions for one or two H atoms at the grain boundary core were determined. It was found that the total energy of the cluster decreased when the H atoms were at that location; thus making it a possible site of H accumulation. An analysis of the orbital interaction revealed that H-Fe bonding mainly involved the Fe 4s and H 1s orbitals. In general, the H drained charge from the first-neighbor Fe atoms. The crystal orbital overlap population curves gave a measure of the Fe–Fe bond weakening due to H segregates at a grain boundary. Some Fe-Fe bonds in the grain boundary plane exhibited a 60% decrease in the overlap population when H was present. Although some H-H association was reveled, no bond was formed between the impurity atoms.

The Electronic Structure and Bonding of H Pairs at Σ = 5 BCC Fe Grain Boundary. S.B.Gesari, M.E.Pronsato, A.Juan: Applied Surface Science, 2002, 187[3-4], 207-17