Strain and coordination effects in the adsorption properties of early transition metals: A density-functional theory study

Strain and coordination effects in the adsorption on early transition metals were studied using density-functional theory. We show that, in contrast to late transition metals, several early transition-metal surfaces with a less than half-filled local $d$ band exhibit lower adsorption energies upon lattice expansion and on low-coordinated sites, in agreement with predictions based on the $d$-band model. This demonstrates that the $d$-band model can be extended to early transition metals. Implications of these results for hydrogen storage materials are discussed.