  We report on a computational study of the clean and oxygen-covered Rh(110)
surface, based on density-functional theory within the local-density
approximation. We have used plane-wave basis sets and Vanderbilt ultra-soft
pseudopotentials. For the clean surface, we present results for the equilibrium
structure, surface energy, and surface stress of the unreconstructed and
$(1\times 2)$ reconstructed structures. For the oxygen-covered surface we have
performed a geometry optimization at $1\over 2$, 1, and 2 monolayer oxygen
coverages, and we present results for the equilibrium configurations,
workfunctions and oxygen chemisorption energies. At half monolayer coverage, we
find that oxygen induces a $(1\times 2)$ reconstruction of the surface, while
at one monolayer coverage the chemisorption energy is highest for the
unreconstructed surface. Our results are rationalized by a simple tight-binding
description of the interaction between the O$-2p$ orbitals and the metal
valence states. The resulting bonds are stronger when established with low
coordinated metal atoms, and give rise to an effective adsorbate-adsorbate
interaction when two oxygen atoms are bound to the same metal orbital.
