Mg(1010)A, and (4 × 2) Mg(1011) periodic surface models with six surface layers where the coordinates of the lowest two layers were constrained to simulate bulk behavior. To find the transition state, we applied the climbing image nudged elastic band (CI-NEB) method as implemented in the transition state tools for VASP (VTST) package. Here, we used five images to represent the minimum energy path (MEP), each separated by a spring constant of 5.0 eV Å-2 . We used the image-dependent pair potential (IDPP) as the initial estimate for the MEP to achieve faster convergence. To confirm stable adsorption positions and transition states, we determined the vibrational frequencies of the diffusing atom and its nearest neighbor atoms along the diffusion path. Stable adsorption sites were required to have no imaginary frequency while transition states must have exactly one imaginary frequency due to a maximum in the potential energy surface in one direction. To calculate harmonic normal modes, we used the dynamical matrix method from the VTST package where the respective atoms were displaced by 0.001 Å in each direction. To this end, we increased the electronic and ionic convergence criteria to 1 × 10 -8 eV and 1 × 10 -8 eV Å-1 , respectively.