To reproduce exhibition to air or a pulsed potential we have employed the reduced OD-Cu systems in the re-oxidation process by depositing oxygen atoms at 300 K on pure Cu reconstructed slab obtained in Figure system. The initial model has 384 Cu atoms and to reach the conversion to Cu2O, 192 oxygen atoms were gradually added to the system at a rate of 1 atom per 3 ps, and initial velocity of 1 Å/ps from 3 Å above the surface atom to avoid the high-speed collision. Initially the oxygen atoms are adsorbed on the surface, and at about 0.06 ns, all the 20 adatoms are sit on the surface. As the content increases, most of the oxygen (103/172) from the deposition source cannot reach the surface due to the repulsion with the surface oxygen. However, after a short time (0.1 ns from the start), the copper atoms are dragged by the surface oxygen, forming a loose structure that allows to accommodate more oxygen atoms, simultaneously some oxygen atoms penetrate deeper into the bulk. After 89 oxygen atoms oxidize the material, the process stops (Figure ). Additional simulation gives the same results even adding 300 oxygen atoms into the system (Figure ). The final thickness of the oxide layer is 16.9 Å (Figure , 46.3 Å to 63.2 Å), in which 6.9 Å of oxide copper are below the original surface (dashed line in Figure , 53.2 Å), and 10 Å above the original surface, the former indicating the diffusion of oxygen to the interior and the latter corresponding to the outward displacement of Cu.