Effect of surface vacancies on the adsorption of Pd and Pb on MgO(100)

Theoretical quantum mechanical calculations have been carried out to establish the effect of surface vacancies on the adsorption of Pd and Pb atoms on the defective MgO(100) surface. The investigated defects included neutral, singly and doubly charged O and Mg vacancies on the (100) surface of MgO. These vacancies played the role of F_s and V_s (n = 0, 1, 2) adsorption centers for a single Pd or Pb atom. From the results of calculations, it is clear that the Pd- and Pb-atom adsorption at the F_s and V_s centers shows different characteristics than at the regular O^2- and Mg²⁺ centers. Drastic changes in geometric, energetic, and electronic parameters are evident in Pd/V_s and Pb/V_s. The effect of F_s⁰ and F_s⁺, which in practice are the most important vacancies, is smaller, yet the adsorption of Pd and Pb at these centers is more energetically favorable than at the regular O^2- center. Of the two metals studied, the atom of Pd is bound by the F_s⁰ and F_s⁺ centers with higher adsorption energies.