First principles study of adsorbed Cun (n=1–4) microclusters on MgO(100): Structural and electronic properties

Abstract

We present a density functional study of the structural and electronic properties of small ${\mathrm{Cu}}_n$ $\text{(n=1,4)}$ aggregates on defect-free MgO(100). The calculations employ a slab geometry with periodic boundary conditions, supercells with up to 76 atoms, and include full relaxation of the surface layer and of all adsorbed atoms. The preferred adsorption site for a single Cu adatom is on top of an oxygen atom. The adsorption energy and Cu–O distance are $E_{\mathrm{S-A}}\text{=0.99\hspace{0.17em}}\mathrm{eV}$ and $d_{\mathrm{S-A}}\text{=2.04\hspace{0.17em}Å}$ using the Perdew–Wang gradient corrected exchange correlation functional. The saddle point for surface diffusion is at the “hollow” site, with a diffusion barrier of around 0.45 eV. For the adsorbed copper dimer, two geometries, one parallel and one perpendicular to the surface, are very close in energy. For the adsorbed ${\mathrm{Cu}}_{\mathrm{3}},$ a linear configuration is preferred to the triangular geometry. As for the tetramer, the most stable adsorbed geometry for ${\mathrm{Cu}}_{\mathrm{4}}$ is a rhombus. The adsorption energy per Cu atom decreases with increasing the size of the cluster, while the Cu–Cu cohesive energy increases, rapidly becoming more important than the adsorption energy.