On Mg(1010)A (Table ), oxygen atom diffusion as calculated with DFT is associated with only minor barriers of 0.12 eV/ 0.05 eV for diffusion between the bdg and the fcc sites (Figure ). With the trained force field, a barrier of 0.10 eV is calculated for diffusion between two fcc sites (Figure ). This result constitutes a significant deviation between DFT and the force field. While in the bdg position is stable, it corresponds to a transition state on the force field's PES. Similar to Mg(0001), the barrier from the oct to the tet position (0.72 eV) is higher than in the reverse direction (0.56 eV) calculated with the force field, while in DFT, the sequence is reversed (0.41 eV and 0.74 eV). For the force field, the low barrier of (0.05 eV) for diffusion from the hcp to the tet position, located below the first surface layer (Figure ), constitutes another deviation. In DFT, we calculated no barrier, causing the oxygen to relax directly to the tet position.