Hydrogen on the Fe (1̄12) surface and hydrogen pairs near bcc mixed (a/2)[11̄1] dislocation: electronic structure

The bonding of H and HH pairs to Fe is analyzed using qualitative electronic calculations in the framework of the atom superposition and electron delocalization molecular orbital cluster (ASED-MO) method. The changes in the electronic structure of bcc Fe upon introduction of a (a/2)[11̄1] mixed dislocation are compared with Fe surfaces. A comparison is drawn with H adsorption at the Fe (1̄12) surface. H in the bulk Fe with dislocations prefers to be near the dislocation core, acting as a trap for H. The Fe atoms are initially more strongly bonded to each other as a consequence of a dislocation introduction (an internal surface); the FeH interaction decreases the FeFe bond strength. The H effect is limited to its first Fe neighbor. An analysis of the orbital interaction reveals that the FeH bonding involves mainly the Fe 4s and H 1s orbitals. A second H is approximated to the minimum energy region when one H is previously positioned. The orbital population analysis reveals some HH association. The HFe interaction is compared with that produced in other defects (vacancies and stacking faults).