Comparison of S, Pt, and Hf adsorption on NiAl(1 1 0)

First-principles periodic slab density-functional theory (DFT) calculations with a plane-wave basis are used to predict the properties of S, Pt, and Hf adsorption on NiAl(1 1 0). Stable adsorption sites are identified, and adsorbate binding energies and structures are predicted. We find that while S adsorbs in a threefold site, the metals prefer to adsorb in the Ni-Ni twofold bridge site. The latter finding is consistent with scanning tunneling microscopy experiments for adsorption of various transition metals on NiAl(1 1 0) by Ho and coworkers. S is predicted to easily diffuse between threefold sites. We find that Pt and Hf both induce significant changes in the local surface structure, changing twofold bridge sites into fourfold coordination sites by drawing next-nearest-neighbor atoms nearly equidistant with the nearest-neighbor atoms. We find Pt favors interaction with Al slightly more than Ni, while Hf shows a particularly strong affinity for Ni compared to Al. We also predict that Hf may diffuse one-dimensionally along Ni rows with a barrier of ≈0.6 eV.