The surface energy is regarded as a measure for the stability of a surface and determines the equilibrium shape of a crystal. In agreement with literature , Mg(0001) is the most stable crystal surface, followed by Mg(101 ! 0)A and Mg(101 ! 1), which differ in our calculations by less than 1 meV•Å -2 (Table ). Mg(0001) lies in the basal plane of the hcp unit cell, which is characterized by a particularly high packing density, resulting in thermodynamic stabilization. At this point, we refer to the work of Tang et al., who established a model to predict the relative stability of magnesium surfaces based on the number of broken basal and non-basal bonds. They also showed that Friedel oscillations are especially present on lowindex Mg surfaces, influencing surface relaxation. On the other hand, on high index surfaces, relaxation is driven by charge depletion and charge smoothing effects. In an embedded atom method (EAM) potential study, Mg (101 ! 1) was considered to be the second most stable surface, which is not the case according to our DFT calculations. Caution is required for Mg(101 ! 0) since there are two possible surface terminations Mg(101 ! 0)A and Mg (101 ! 0)B, which are shown in SI Figure . Mg(101 ! 0)B differs from Mg(101 ! 0)A by one missing row and is characterized by parallel atomic lines making deep channels. Mg(101 ! 0)A also has channels, but not as distinct as in Mg(101 ! 0)B. Surface energies calculated with the BEEF-vdW functional are generally lower but have the same stability sequence. All PBE results are within the error range of the BEEF-vdW functional. Further surface energies (that also entered the following Wulff construction) and a literature data summary are provided in SI Table .