NiAl(110) surface: First-principles determination of the rippled relaxation

Abstract

The relaxation pattern in the NiAl(110) surface and its magnitude are determined quantitatively with use of first-principles total-energy calculations based on the mixed-basis ab initio pseudopotential method. Minimization of the surface energy in a five-layer slab geometry yields a rippled relaxation in the outermost surface layer. Ni atoms contract into the bulk by 6.9% of an interlayer spacing and Al atoms expand out to the vacuum region by 6.6%. The calculated results are in very good agreement with recent results obtained by two independent experiments, low-energy electron diffraction (LEED) and medium-energy ion scattering (MEIS). We discuss the driving mechanism behind this rather complicated relaxation pattern in a both qualitative and quantitative manner by concentrating our attentions on the crucial roles of the localized d electrons in Ni sites and of the weakly bound s,p electrons around Al sites in the vicinity of the surface layer.