Electronic structure and bonding of hydrogen in a screw dislocated bcc Fe

The bonding of H-Fe is analyzed using qualitative electronic calculations i n the framework of the atom superposition and electron delocalization orbit al cluster method (ASED-MO). The changes in the electronic structure of bcc Fe upon introduction, a screw dislocation are compared with Fe surfaces. A comparison is drawn with H adsorption at Fe (112) surface and Il absorptio n in the bulk Fe with a dislocation. The results suggest that the detriment al effect of H on the Fe-Fe bonds in a screw dislocation is almost half-sev ere than in other defects, such as an edge dislocation or vacancy and it is limited to its first neighbor. An analysis of the orbital interaction reve als that Fe-H bonding involves mainly the Fe 4s and H 1s orbitals. When H i s in the bulk, the region near screw dislocation core is much more repulsiv e than in a normal Fe lattice. These results allow us consider that H accum ulation could be less favorable near a screw dislocation than an edge dislo cation. (C) 2001 Elsevier Science B.V. All rights reserved.