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 agreement with previous plane wave density functional and empirical tight binding calculations but is significantly different to either of the proposed structures 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 the (100) or (110) surfaces confirming that it is the least stable low index termination of rutile TiO2. Finally, we examine the electronic structure of the relaxed surface and find no evidence for the presence of band gap states as reported in early photoemission experiments and tight binding calculations. The current results suggest that such states will only occur on the defective surface and are likely to be localised Ti3+ states induced by oxygen reduction. (C) 2000 Elsevier Science B.V. All rights reserved.