Here G def and G ideal are the Gibbs free energies for surfaces with and without defects, respectively. They are calculated here including vibrational and electronic entropy as well as zero-point corrections in harmonic approximation. The last term in Eq. 2 accounts for the stoichiometry changes, i.e., ∆n j is the difference in the number of atoms of species j, and µ j the respective chemical potential. In case of hydrogen desorption, the H chemical potential change ∆µ H with respect to an isolated molecule has been calculated in the approximation of a two-atomic ideal gas in dependence on partial pressure p and temperature T following