First-principles study of water adsorption on Ci-Al₂O ₃(0001): Influence of hydrogen isotope

Adsorption of H₂O on the α-Al₂O ₃(0001) surface was studied by means of a first-principles calculation based on density functional theory (DFT). We also investigated the behavior of the isotope exchange by substituting a protium atom with deuterium or tritium. The oxygen atom of H₂O adsorbs on the Al atom of the outermost surface layer, the entire water molecule is slanted at the direction of a hollow site, and a molecular plane is nearly parallel to the surface. The adsorbed states are mostly due to coupling of lone-pair electrons of H ₂O with the empty p orbitais of the Al atom of surface. The behavior of dissociation for H₂O is clarified from molecular dynamics simulations, indicating that the second neighbor oxygen atom is more preferable adsorption site for dissociation than the nearest neighbor oxygen atom on the surface.