Interaction of hydrogen with the Be(0001) surface

Extensive first-principles calculations of the H-Be interaction reveal that novel H-surface vacancy structures dominate the high-coverage regime, from 2/3 to 1 monolayer (ML). At 1 ML the low-energy structure is a honeycomb of Be vacancies each decorated by three bridge-bonded H's tilting inward. At 2/3 ML the H's tilt in toward linear trenches organized in a 3×{}1 structure. At low coverages H prefers ordinary hcp threefold sites. A combination of the three structural models explains most of the experimental results. The adsorption of H in subsurface sites is shown to be unlikely.