Reconstructions and faceting of H-covered Al(111)

First principles calculations show that H overlayers induce a honeycomb vacancy reconstruction on Al(111). Above one ML H coverage, Al(111) facets into surfaces vicinal to (111), with {100} faceted single and double steps and vacancies on the {111} terraces. These H induced reconstructions are stable because H binds more strongly to {100} than to {111} facets. Faceting of Al(111) explains step bunching in H-mediated epitaxy of Al(111). H-covered Al(100) is stable against faceting.