Adsorbate-Induced Surface Stress: Phonon Anomaly and Reconstruction on Ni(001) Surfaces

Ab initio all-electron calculations for carbon and oxygen chemisorbed on nickel clusters indicate that the charge redistribution induced by the adsorbate causes repulsive stresses between the metal surface atoms. Using lattice-dynamics calculations we show that these stresses can account for the observed $S_4$-phonon anomaly with $c(2\mathrm{}\times 2)$ oxygen overlayers, and also explain the carbon-induced surface reconstruction, via a softening of the $A_2$ mode at $X$ The reconstruction has also been reproduced directly by total-energy calculations with use of a suitable cluster.