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Density Functional Theory Study on Hydrogen Adsorption on Be(0001) Surface

We report on density functional theory (DFT) total-energy calculations within the generalized gradient approximation for the adsorption of hydrogen onto Be(0001) surface. To investigate the atomic geometries and stability with different hydrogen coverages for this system, we changed the atomic hydrogen coverage from 0.06 to 1.33 monolayer (ML) using various surface supercell geometries. The calculations showed that the adsorption sites have a strong dependence on hydrogen coverage. The adsorbates mainly occupied fcc and hcp hollow sites below 0.67 ML. At 0.78 ML the hydrogen atoms were adsorbed on hollow and bridge sites while for the higher coverage range (ca 0.89-1.00 ML) the hydrogen atoms were adsorbed onto the tilted bridge sites, i.e., a bridge site with a small deviation towards the hollow position. From 1.11 to 1.33 ML, the adsorbed hydrogen atoms were located at hcp and bridge sites, and some Be surface atoms were expanded. All these adsorption configurations were found to be energetically favorable with a H2 reference point fixed on H2 molecule. Further total-energy calculations based on a p(3×3) geometry did not revealed any stable or energetically favorable adsorption geometry versus the H2 molecule beyond a hydrogen coverage of 1.33 ML.