Adsorption of small molecules on the anatase(100) surface

The adsorption of NH3, H2O, and NO on the (1 0 0) surface of TiO2 anatase is studied with the semiempirical SCF MO method MSINDO. The (1 0 0) surface is modeled with clusters (TiO2)(n)(H2O)(m) (n = 33-132, m = 17-48) where H and OH groups serve stoichiometrically for saturation. Fivefold coordinated titanium surface atoms, which are Lewis acid sites, are considered as adsorption sites, and the effect of cluster size and surface relaxation on the calculated adsorption energies and geometries is investigated. Only a small dependence on the cluster size and on surface relaxation is found for the adsorption energy. By comparison with experiment and ab initio and density functional theory calculations it is shown that MSINDO can reproduce literature data with satisfactory accuracy. (C) 2004 Published by Elsevier B.V.