Fig. 1. Fragment of a α-Al₂O₃(0 0 0 1) surface displaying four types of oxygen triangle sites.

Fig. 2. Cluster models M/[Al₄O₆]/(Al^pp*)₆ (1) and M/[Al₁₀O₁₅]/(Al^pp*)_n (2; n=13,15) used to analyze the interaction of the metal atoms M (M=Pd, Pt) with the surface α-Al₂O₃(0 0 0 1).

Fig. 3. Change Δμ=μ−μ_eq of the dipole moment of clusters modeling the adsorption of Pd and Pt at the site o as a function of the height z of the adatom above the nearest O atom. μ_eq is the dipole moment at equilibrium, μ is the dipole moment calculated when only the Pd atom is displaced and all other atoms are kept at equilibrium positions. Solid line––substrate cluster at equilibrium geometry of the adsorption complex; dashed line––substrate cluster at the geometry optimized for a “clean” surface; dashed-dotted line––substrate cluster at the equilibrium position of the adsorption complex, but the Al1 atom nearest to the Pd atom placed at the position in the cluster which models a clean surface.

Table 1. Nearest-neighbor interatomic distances r, binding energies E_b, energy gain due to substrate relaxation ΔE_b=E_b(r)−E_b(f), accompanying vertical displacements Δz of the Al1 and O1 atoms, and dynamic dipole moment ∂μ/∂z for adsorption of a Pd atom on the EPE embedded clusters [Al₄O₆]/(Al^pp*)₆ (1) and [Al₁₀O₁₅]/(Al^pp*)_n (2, n=13 for u, m and n=15 for d, o), modeling different sites of α-Al₂O₃(0 0 0 1)

Table 2. Nearest-neighbor interatomic distances r, binding energies E_b, energy gain due to substrate relaxation ΔE_b=E_b(r)−E_b(f), accompanying vertical displacements Δz of the Al1 and O1 atoms, and dynamic dipole moment ∂μ/∂z for adsorption of a Pt atom on the EPE embedded clusters [Al₄O₆]/(Al^pp*)₆ (1) and [Al₁₀O₁₅]/(Al^pp*)_n (2, n=13 for u, m and n=15 for d, o), modeling different sites of α-Al₂O₃(0 0 0 1)