To understand the structure of the oxidized nanoparticle we plot the oxygen distribution profiles in Figure . The plots represent the spherical density or concentration of oxygen atoms as a function of distance from the center of mass. As the pressure increases, the amount of oxygen penetrating inside the nanoparticle increases, first in subsurface sites at 10 -5 atm, and then in the core region for pressures above 10 -2 atm. This is in agreement with the previous coordination number analysis shown in Figure . Additionally, the same plots reveal a significant amount of lattice strain caused by subsurface and core oxygen atoms at higher pressures. At a pressure of 10 -15 atm, the outer shell boundary is clearly visible and located approximately 11 Å away from the center of mass. As the pressure increases, the boundary becomes less defined and oxygen atoms are found at distances up to 20 Å away from the center of mass.