  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.
