Dissociative adsorption of water on the Si(001) surface: A first-principles study

The adsorption of water on the Si(001) surface is studied by using density-functional total-energy calculations within the generalized gradient approximation. We find that water can adsorb molecularly on the down atom of the Si dimer, but a dissociative adsorption wherein OH (H) forms a bond to the down (up) atom of the Si dimer is more favored over the molecular adsorption (by 1.8 eV). The decay of the molecular state to the dissociative state occurs via a transition state with the energy barrier of only 0.15 eV. While the interaction between water molecules is repulsive, that between dissociated OH species is attractive by hydrogen bonding.