5 -5  0  5  10 ionic z coord. (a 0 ) site Na O Mg -5  0  5  10 ionic z coord. (a 0 ) Mg site -5  0  5  10  0.5  1  1.5  2  2.5 ionic z coord. (a 0 ) time (ps) hollow site  0  0.5  1  1.5  2  2.5  0  0.1  0.2  0.3  0.4 kinetic energy (ev) time (ps)  0  0.1  0.2  0.3  0.4 kinetic energy (ev)  0  0.1  0.2  0.3  0.4 kinetic energy (ev) Na Na trans. Na vert. O Mg FIG. 3: Time evolution of the ionic coordinates and kinetic energies E$_{kin}$ for the deposition of a Na monomer on MgO(001) with initial kinetic energy E 0 kin = 0 . 136 eV, impinging on various sites : O site (top), Mg site (center) and hollow site (bottom). Left : z coordinates of Na (thick line), Mg (thin curve), and O (gray line) cores. Right : Total E$_{kin}$ of Na (thick gray or red curve), lateral E$_{kin}$ of Na (magenta dots), vertical E$_{kin}$ of Na (black dashes), and total E$_{kin}$ of Mg (thin dark or blue curve) and O (thin light or green curve) cores. at an hollow site. We see again the immediate reflection at impact time associated with fast energy transfer. Less energy is transferred than on the other sites (see upper and middle panels) and thus the bounce-back has a much larger amplitude than in both other cases. The Na mo- tion remains strictly perpendicular to the surface as prac- tically no lateral kinetic energy can be seen. The vertical kinetic energy is almost approaching zero because the departing Na atom has to work against the polarization potential. The case is at the limits of our box size and energy resolution such that we cannot decide whether the atom will finally escape with extremely small kinetic en- ergy, or will bounce back and relax to an adsorption site on a very long time scale. Nevertheless, we find it worth- noting that the hollow site seems sufficiently attractive to hinder deflection towards the still more attractive oxygen site. The analysis of section III A has shown the importance of surface site nature in the deposition process. Deposit- ing an extended object such as a cluster will lead to a B. Cluster deposition 1. The case of symmetric Na$_{8}$