The structure and bonding of carbonate on Ag(1 1 0): a density-functional theory study

The local structure of the carbonate species, CO3, on Ag(1 1 0) has been investigated using density functional theory (DFT) slab calculations. The results show that adsorption on top of the added Ag rows induced by the carbonate formation, proposed on the basis of early scanning tunnelling microscopy (STM) studies, is not energetically preferred. Instead, adsorption is in a site to one side of these added rows and above an Ag atom in the outermost un-reconstructed layer, as suggested in later STM work and also found in a scanned-energy mode photoelectron diffraction (PhD) investigation. The DFT calculations give structural parameter values which are mostly in excellent agreement with the results of the PhD study, but show a larger (20°) tilt of the molecular plane from the surface, still broadly consistent with X-ray absorption fine structure data. The carbonate thus bonds to the (1 1 1) nanofacet of the added-row structure through the O atoms, one O atom bridging two adjacent added row atoms, while the other two O atoms are off-atop Ag atoms in the layer below. The bonding involves significant (approximately 0.5 e) electron charge transfer to the O atoms of the carbonate.