Ab initiocalculations of hydrogen adsorption on (100) surfaces of palladium and rhodium

We report an all-electron density-functional-theory study of the interaction of hydrogen with Pd(100) and Rh(100) surfaces. We use the local-density approximation for the exchange-correlation energy functional and the full-potential linear-muffin-tin-orbital method. Various coverages, between {Θ}=0.25 and {Θ}=2 are considered. In particular, we discuss the adsorption energies, stable adsorption sites, adsorption-induced surface relaxations, and the work-function changes. The results show that for coverages {Θ}{≤}1 at Pd(100) the fourfold hollow site is energetically favorable. For higher coverages it is predicted that the additional hydrogen goes subsurface. The work function is found to increase with coverage up to {Θ}=1 and for higher coverages (i.e., when the subsurface sites get occupied) it remains roughly at the {Θ}=1 level. Hydrogen adsorption at Rh(100) is found to be very similar to Pd(100) up to {Θ}=1. The results are compared to available experimental data as well as to other calculations.