All-electron local-density theory of the rippled NiAl(110) surface

The structural and electronic properties of the rippled NiAl(110) surface are investigated using the all-electron total-energy local-density full-potential linearized augmented-plane-wave method. Surface states are found to have ≃1.3-eV binding energies at $\overline{\Gamma }-$ in excellent agreement with the Auger spectra data. The geometry of the rippled surface and the optical-phonon frequency at $\overline{\Gamma }$ are determined by means of frozen phonon calculations. In good agreement with recent experiments, we find the rippling to be 0.20 Å for the composite Ni-Al surface layer with Al displaced outwards relative to the contracted Ni layer. A possible mechanism behind the surface rippling is discussed in terms of charge-transfer effects and electrostatic neutrality. The charge densities and calculated work functions for the relaxed and unrelaxed surfaces are also reported and discussed in relation to this mechanism.