On the MgO(001) surface, Co adatoms preferentially adsorb on the oxygen sites, with an equilibrium distance of 184 pm from the surface. This result agrees with a previous DFT study. For Co/Mg(O)(001), dispersion computed using the D3 correction to PBE contributes only 15% to the total adsorption energy. The total magnetic moment µ is 3 Bohr magneton, consistent with a spin S = 3/2 ground state. This magnetic moment is lo- with fully quenched orbital angular momentum rather than with the non-aufbau configurations expected for its ground state (see Figure ). This suggests that DFT-based methods fail to adequately capture the true ground state of Co adatoms. The HSE06 density of states is similar; however, the hybrid-GGA functional predicts that the d z 2 orbital is no longer degenerate with the d xz , d yz orbitals, better reflecting the expected d-orbital splitting in a linear coordination environment (Figure ). These results also closely align with the density of states reported in Ref. 54, obtained using PBE+U .