√7R19.1° superlattice of Ar/Ag(111) -: art. no. 033407

Recent observations of a higher-order-commensurate lattice of argon physisorbed on Ag(111) are discussed. The source of the registry energy and the positioning of the unit cell with four Ar atoms in hi,oh-symmetry low-coordination sites are attributed to a special case of the Novaco-McTague mechanism for orientational epitaxy. The importance of measurements of the differences of adatom-substrate distances in the unit cell is emphasized.