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| - Structures of Glycine, Enantiopure Alanine, and Racemic Alanine Adlayers on Cu(110) andCu(100) Surfaces
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| - We have determined the structures of dense adlayers of glycine and alanine on the Cu(110) and Cu(100)surfaces using plane wave density functional theory. These calculations resolve several experimentalcontroversies regarding these structures. Glycine exists on Cu(110) as a single adlayer structure, while onCu(100) two distinct glycine adlayers coexist. The glycine structures serve as useful starting points forconstructing alanine adlayer structures. We considered separately the adsorption of enantiopure alanine andracemic alanine on each surface. Adlayers of enantiopure alanine are found to be closely related to the adlayersobserved for glycine. Racemic alanine adlayers on Cu(110) are structurally analogous to those observed forglycine on this surface and adopt a pseudo-racemate ordering. On Cu(100), in contrast to glycine, racemicalanine is found to adopt a single adlayer structure that is an ordered racemate. Spontaneous segregation ofmolecular enantiomers does not occur in racemic adsorbed mixtures on either surface. Consideration of theorientationally distinct domains that may exist for each adlayer on these surfaces provides important informationfor the interpretation of the adlayer domain boundaries that are commonly observed in scanning tunnelingmicroscopy images of amino acid adlayers. Examining this set of amino acid adlayers provides useful insightinto the range of subtle behaviors that can arise in these and related systems where chiral molecules formordered adlayers on flat metal surfaces.
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