The physical and electronic structure of the rutile (001) surface

We present the relaxed structure of the (001) surface of TiO2 obtained from fully converged ab initio calculations using both Hartee-Fock and density functional theories. The calculated surface structure is in reasonable agre ement with previous plane wave density functional and empirical tight bindi ng calculations but is significantly different to either of the proposed st ructures based on LEED-IV experiments. We discuss possible reasons for the discrepancy with the LEED-IV results. The current calculations also reveal that the (001) termination has a significantly higher surface energy than t he (100) or (110) surfaces confirming that it is the least stable low index termination of rutile TiO2. Finally, we examine the electronic structure o f the relaxed surface and find no evidence for the presence of band gap sta tes as reported in early photoemission experiments and tight binding calcul ations. The current results suggest that such states will only occur on the defective surface and are likely to be localised Ti3+ states induced by ox ygen reduction. (C) 2000 Elsevier Science B.V. All rights reserved.