Origin of the Coverage-Dependent Vibrational Shift for O on Ni(100)

Abstract

The $p(2\mathrm{}\times 2)$ and $c(2\mathrm{}\times 2)$ coverages of O on Ni(100) are studied with a cluster model. The $p(2\mathrm{}\times 2)$ coverage is modeled by the addition of a single O at a fourfold site. The $c(2\mathrm{}\times 2)$ is modeled by the explicit inclusion of four additional O atoms. Consistent with electron energy-loss spectroscopy results, the O-Ni vibration is 85 ${\mathrm{cm}}^{-1\mathrm{}}$ lower for the $c(2\mathrm{}\times 2)$ cluster than for the $p(2\mathrm{}\times 2)$. The height of O above the surface is 0.11 Å smaller for the $c(2\mathrm{}\times 2)$ coverage. The nature of the O-to-Ni bonding is similar for both coverages.