In order to reveal the mechanism of the electrochemical processes of cathode surfaces in ultrapure water, first-principles molecular-dynamics simulations of chemical reaction on the Al(001) surfaces interacting with H atoms, H2O molecules and OH molecule were carried out on the basis of the Kohn-Sham local-density-functional formalism. A plane-wave basis set was used, and the cut-off energy is 594eV(64Ry). A norm-conserving pseudopotential was also used. We adopt the standard molecular-dynamics method for the optimization of the ionic system and the preconditioned conjugate-gradient (CG) method for the quenching procedure of the electronic degrees of freedom. We determined the optimized atomic configurations and electronic distributions for H atom and H2O or OH molecule chemisorbed Al(001) surfaces. It was confirmed that an H atom reacts with H2O molecules on the Al(001) surface to produce an OH molecule. Chemisorption of an OH molecules and H atoms to the Al(001) surface atom breaks the back-bonds and side-bonds, and the Al(001) surface atom is etched as an AIH2OH molecule. From these simulated results, we concluded that the electrochemical etching of Al(001) cathode surface in ultrapure water is induced by H atoms and OH molecules.
