Ab Initio Modeling of the Metal−Support Interface:  The Interaction of Ni, Pd, and Pt on MgO(100)

Abstract

The interaction of Ni, Pd, and Pt on MgO has been investigated using cluster models and a variety of ab initio techniques. The case of a single Pd atom with acidic and basic sites of the MgO(100) surface has been chosen to test the adequacy of different ab initio wave functions and DFT techniques. Both approaches result in a similar description but only if large basis sets, including high angular momentum terms, and extensive treatment of the many-body effects are accounted for in the ab initio cluster model wave function. The DFT results appear to be more stable and less dependent on the basis sets. When properly compared, both approaches lead to the same conclusion. Pd interacts in a rather weak way with the acidic sites, but a moderately large interaction is predicted for interaction above the basic sites. Next, the interaction of Ni, Pd, and Pt on the basic sites of the MgO(100) surface is considered. The general trend is that the interaction energy increases from Ni to Pt. The nature of the bond is rationalized by analysis of the dipole moment curves and of the molecular orbitals.

Interaction of Pd withα−Al2O3(0001):

“…23,[25][26][27][28][29] The ideal, undefective MgO͑100͒ surface is a prototype of such a simple system. 12 In order to construct a single cluster model representation of the relaxed ␣-Al 2 O 3 (0001) surface the following strategy was used.…”

“…In general the BSSE is important in weak interactions only but in the special case of oxide surfaces the diffuse nature of the oxide anion results in BSSE's of several tenths of an eV. 12,23,[25][26][27][28][29] Therefore, only the BSSE corrected adsorption energy computed following the standard BoysBernardi counterpoise method 44 is reported in the different tables. This BSSE corrected adsorption energy is computed as E ads ϭE͑PdϪcluster͒ϪE͑clusterϩPd basis at R e ͒ ϪE͑Pdϩcluster basis at R e ͒.…”

“…The calculated values show an unexpected dependence on the choice of computational method. 23,25 This dependence is particularly marked in density-functional-theory ͑DFT͒-based methods. In fact, for Cu on basic sites of MgO͑100͒ it has been shown that the interaction energy obtained from different gradient-corrected exchange-correlation functionals may differ by a factor of 2.…”

“…On the MgO surface, the computed adsorption energy for Pd adsorbed on the basic sites is almost three times the one calculated for Pd adsorbed on the acidic sites and the same behavior is also followed by different adsorbed metal atoms. 23,[27][28][29] However, the data discussed so far concerning the adsorption of metals on the ␣-Al 2 O 3 (0001) surface indicates that even for a clean and nearly perfect surface different surface sites may compete. The order of stability of metal adatoms on the clean ␣-Al 2 O 3 (0001) surface may influence the growth mechanism of the metal cluster and has implications for the diffusion of metal atoms on bulk ␣-Al 2 O 3 .…”

Surface model and exchange-correlation functional effects on the description of Pd/α-Al2O3(0001)

“…The importance of establishing the influence of these approximations is also manifest in previous studies of the interaction of transition metals on the surface of simple oxides. The previous work of Lopez et al 18 on the interaction of Pd with MgO͑100͒ strongly suggests that in DFT methods the influence of the choice of exchangecorrelation functional can be very significant. For the adsorption of Cu on MgO͑100͒ the validity of the cluster model has been demonstrated explicitly.…”