From equilibrium simulations at different temperatures, until the equilibrium temperature increases to 600 K, the diffusion of oxygen from inside to the surface was observed in the equilibration time in this work, i.e., 1 ns (the first oxygen appears on the topmost layer in 0.72 ns). Although the formation of Cu2O surface is more favorable, the sluggish kinetics of oxygen diffusion could slow down the process. Figure shows the diffusion coefficient of oxygen, DO, in pristine Cu2O bulk as obtained from the meaningful data of mean squared displacement (MSD) at high temperatures (1400 K to 1800 K).