Effect of embedding and cluster size on the ab initio study of potassium adsorption at rutile(110)

The results of Hartree-Fock ab initio model calculations for the adsorption of a single potassium atom on a bridging oxygen site of the rutile(110) surface are presented. The surface is simulated with small clusters Ti2O4 and Ti4O8, either embedded in a finite array of total ion potentials and point charges or saturated with H, OH, and H2O. The effect of the different embedding techniques on physical aspects of the adsorption process is discussed in terms of electronic structure and energetics. Comparison of available experimental data and previous theoretical studies with the present results show that medium-sized model clusters give a reasonable description of the adsorption process, independent of the embedding method. For very small models, even the qualitative picture of the K-TiO2 interaction changes when different embedding techniques are used. These results can be generalized to develop rules for designing cluster models for metal adsorption on futile surfaces. (C) 1999 John Wiley & Sons, Inc.