First, the present calculations confirm the preference of magnesium to crystallize in a hcp crystalline structure at ambient conditions, with surface terminations Mg(0001), Mg(101 ! 0)A, and Mg(101 ! 1) being, in this order, most stable. Interestingly, the surface proportions in a nanocrystal are quite different. According to the Wulff construction, Mg(101 ! 1) has the largest share of the surface with a surface fraction of about 50%, while the remaining area is distributed evenly between Mg(0001) and Mg(101 ! 0)A, as shown in Figure . The Wulff construction clearly illustrates that diffusion properties must be discussed for all three surfaces collectively and cannot be limited to the thermodynamically most stable surface Mg(0001), as done in previous studies. Furthermore, we found the highest adsorption energies for an Mg atom on the occurring surfaces for the hollow site on Mg(101 ! 1) and the ontop-bottom site on Mg(101 ! 0)A. Adsorption energies on Mg(0001) are about 40% lower, indicating primary adsorption to take place on Mg(101 ! 0)A and Mg(101 ! 1). Preferred adsorption on Mg(0001) occurs on the fcc site, which is valid for a trimer, too. Adsorption on hcp sites is energetically favored starting from heptamers.