Oxygen atoms on the (1 1 1) surface of coinage metals: On the chemical state of the adsorbate

We employed periodic slab model calculations to examine the charge state of atomic oxygen species adsorbed on Cu(1 1 1), Ag(1 1 1) and Au(1 1 1) surfaces. Threefold sites are computed to be preferred on all three substrates. Similarities and differences in the ionicity of adsorbed O are analysed using charge density difference plots, work function changes, dipole moment curves and topological charge analysis. Performance of these methods to characterise chemical bonding is discussed. In agreement with the metal electronegativity values, large negative charge of similar size is found on oxygen in the O/Cu(1 1 1) and O/Ag(1 1 1) systems, whereas O on Au(1 1 1) is significantly less ionic.