The first steps of molecular oxygen adsorption and further incorporation on a Si(100)-p(2×2) surface are described here using density functional theory for the atomistic mechanisms. In this study, our aim is to combine this approach with kinetic Monte Carlo simulations to get an insight into the description of the oxide growth on silicon surface. We detail the reaction paths and corresponding energy barriers for the atomistic mechanisms: oxygen dissociation, adsorption and migration. We then explain how these data emanating from first principle calculations can be implemented in our kinetic Monte Carlo code OXCAD.