First principles study of adsorbed Cu_n (n=1-4) microclusters on MgO(100): structural and electronic properties

摘要

We present a density functional study of the structural and electronicproperties of small Cu_n (n=1,4) aggregates on defect-free MgO(100). Thecalculations employ a slab geometry with periodic boundary conditions,supercells with up to 76 atoms, and include full relaxation of the surfacelayer and of all adsorbed atoms. The preferred adsorption site for a single Cuadatom is on top of an oxygen atom. The adsorption energy and Cu-O distance areE_S-A = 0.99 eV and d_S-A = 2.04 Angstroems using the Perdew-Wang gradientcorrected exchange correlation functional. The saddle point for surfacediffusion is at the "hollow" site, with a diffusion barrier of around 0.45 eV.For the adsorbed copper dimer, two geometries, one parallel and oneperpendicular to the surface, are very close in energy. For the adsorbed Cu_3,a linear configuration is preferred to the triangular geometry. As for thetetramer, the most stable adsorbed geometry for Cu_4 is a rhombus. Theadsorption energy per Cu atom decreases with increasing the size of thecluster, while the Cu-Cu cohesive energy increases, rapidly becoming moreimportant than the adsorption energy.