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.