By means of tight-binding quenched-molecular dynamics simulations. we have investigated the adsorption and the incorporation of a Co atom on the reconstructed Au(111)-(22 x root3) surface, The activation energies for the diffusion across the discommensuration Lines are slightly larger than in the coherent regions of f.c.c. and h.c.p. stacking. Upon a relaxation effect, the adatom experiences the lowest energy minimum on top of the discommensuration lines. Consistently, the lowest incorporation energy is obtained in the same region of the reconstructed surface, Because of the natural size mismatch between Co and Au. the incorporation is much more favourable in the most contracted parts of the reconstruction. (C) 2002 Elsevier Science B.V. All rights reserved.