Alloying Coordinative Unsaturation versus Increased Overlap Energies

Alloying Coordinative Unsaturation versus Increased Overlap Energies 

The altered surface properties of metal alloys can also be interpreted in terms of valence electron delocalization changes. Delocalization changes because of altered metal atom-metal atom overlap energies and different positions of the 

The calculated dissociation energy of H2 increases linearly with decreasing energy e. Because of the mismatch between metal atom radii and substrate metal atom distances, the overlayer metal-metal atom distances can he very different compared to the case where the metal overlayer and substrate are the same 

The increased covalent interaction between Ni and Ru balances the loss in electron delocalization due to the stretched distance between the Ni atoms. Hence, the interaction energies with H are unaltered. However, because of the increasing covalent interaction with W, which has more extended d-atomic orbitals and a lower d-valence electron count compared to Ru, the Ni d-valence electron delocalization increases for the Ni/W system. Hence, the interaction energy with H is found to decrease. 

The d-valence band that is initially closer to the Fermi level will obtain the lower electron occupation. 

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