The effect of interstitial hydrogen on the electronic structure of Fe-Pd alloys

The electronic structure and bonding in Fe-Pd alloys were computed using a tight binding method. Two phases have been identified for these alloys, a high temperature fcc and a low temperature fct structure. The hydrogen absorption turns out to be a favorable process in both structures. The hydrogen at tetrahedral interstitial site for the fct structure is 2.2 eV more stable than that impurity atom located at an octahedral interstitial site in the fcc structure.The density of states curves show a peak below the d metal band which is made up mostly of hydrogen based states (>50% H_1s) while the metal contribution includes mainly s and p orbitals.In the fcc structure, both Fe-H and Pd-H bonds are developed while the Fe-Pd interface shows antibonding filled states near the Fermi level. When the fct phase is considered, the Fe-H overlap population (OP) decreases, while the Pd-H remains similar to the previous case. The Fe-Fe OP decreases and the Pd-Pd bonds are almost unaltered. The interfacial Fe-Pd bonds are almost unaffected by hydrogen. The band structure of the hydrogenated alloys in the fcc and fct phases were also computed.