Coin metal adsorption on defective MgO(001) surface: Ab initio study

First principles slab calculations have been performed for Ag and Cu adsorption on periodically distributed point defects (a single O^2- or Mg²⁺ vacancy per 2×2 surface supercell) on the non-polar MgO(001) substrate. Using the procedure implemented in the CRYSTAL-03 code, both F_s and V_s centers were modeled by retaining in the vacancy the basis set of the missing O^2- and Mg²⁺ ions, respectively, with the local relaxation of the nearest substrate ions. Adsorption of metal atom over the F_s center (2.4 eV vs. 2.1 eV per Cu and Ag adatoms, respectively) is much stronger as compared with regular O ^2- sites (0.6 eV vs. 0.4 eV, respectively). The F_s center donates a substantial charge towards Ag and Cu adatoms (0.3-0.4 e) as well as forms covalent bonds with them, with similar bond populations. When metal adatom approaches the V_s center, it donates 1.0-1.1 e towards the nearest surface O^2- ions and its binding energy (10.0 eV vs. 9.6 eV per Cu and Ag adatoms) is markedly larger than that over the F_s center. Moreover, the interfacial distance in the former case is quite small (0.16-0.23 Å), thus metal adatom almost substitutes a missing Mg²⁺ ion.