Oxygen plays a crucial role in the iron corrosion process, promoting surface passivation. It forms iron oxides and hydroxides and participates in the cathodic reaction, which reduces the oxygen to water in the overall corrosion process. The effects of dissolved oxygen by replacing one water molecule with an oxygen molecule are investigated. Figure reports the structural variation before and after a water molecule is replaced with an oxygen molecule through optimization. It is revealed that the oxygen dissociates and adsorbs on the Fe(100) surface.