Water Adsorption on the Reconstructed (001) Chalcopyrite Surfaces

The interaction of water molecule with the reconstructed (001) chalcopyrite surfaces has been investigated by means of density functional calculations. All of the calculations were performed using periodic boundary conditions with SIESTA code. The structural parameters were compared with those obtained through PWscf code in order to evaluate the pseudopotentials and numerical basis set developed for this work. Two different surfaces were studied, namely, sulfur-terminated, (001)-S, and metal-terminated, (001)-M. The (001)-S surface reconstructs, forming disulfide dimers with a bond length of 2.23 angstrom. The (001)-M surface reconstructs, reordering the metal atoms in order to form planes of metal atoms and interlaced sulfur atoms. Different adsorption sites for the water molecule were investigated. The dissociative mechanism of the water molecule has also been analyzed in detail. For the (001)-S surface, the water adsorption on the iron atom is the preferred mechanism. The dissociative mechanism leads to structures which are, at least, 13 kcal mol(-1) higher in energy than the water adsorbed on iron atom. For the (001)-M surface, no minima in the potential energy surface were found, and the water molecule prefers to form a hydrogen bond with the sulfur atoms. The dissociative mechanism for the water adsorption on (001)-M surface is thermodynamically unfavorable. The metal-alloy-like structure underneath of the sulfur atoms and the unfavorable water adsorption indicate that the surface presents some hydrophobic character. The influence of the water molecule in the reconstruction of the (001) chalcopyrite surface and in its reactivity is discussed.