A study was made of the adsorption of small metal aggregates Mn (M = Cu, Ag, Au; n = 2, 3) on the ideal MgO(001) surface, as well as on O vacancies, using a first-principles computational approach. A generalized-gradient density functional was used, combined with cluster embedding in an elastically polarizable environment which provided an accurate description of substrate relaxation. In the same way as single adsorbed atoms, metal moieties on regular O2- surface sites were polarized and interacted mainly by electrostatic attraction; counteracted by Pauli repulsion. However, adsorption on vacancies involved some transfer of electron density to the adsorbate; particularly for Au2. The cluster results for Cu2 and Cu3 on regular O2- sites agreed quantitatively with previous results for periodic slab models. The adsorption energy per atom decreased from dimers to trimers, in accord with the fact that metal-metal cohesion predominated over metal-oxide interaction. Compared to regular sites on flat terraces, dimerization was not particularly favorable at Fs sites and was unfavorable at Fs+ sites.

Adsorption of Dimers and Trimers of Cu, Ag, and Au on Regular Sites and Oxygen Vacancies of the MgO(001) Surface - a Density Functional Study using Embedded Cluster Models. C.Inntam, L.V.Moskaleva, K.M.Neyman, V.A.Nasluzov, N.Rösch: Applied Physics A, 2006, 82[1], 181-9