Electronic structure of a hydrogen impurity near a (001) Pd surface

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Abstract
We discuss the adsorption and absorption of light impurities (H) near a transition-metal surface (Pd), within the framework of the electronic structure of interstitial impurities. We derive the band structure and total energy of the system H/Pd(001) in a tight-binding model, taking into account s,p,d orbitals of Pd. We obtain the relative stability of the various sites (tetrahedral and octahedral sites), relative to their position to the surface, from adsorption to absorption. The ‘‘bridge’’ geometry is found to be the stablest adsorption site with an energy in agreement with experiment. Some ‘‘subsurface’’ sites are also very stable ones. The coupling strength between the 1s orbital of hydrogen to the 5s orbital of Pd is an essential parameter. We argue that the interactions between H atoms, even at small finite concentration, can qualitatively alter the results obtained in the infinitely dilute impurity result.