EFFECT OF RELAXATION ON THE ENERGETICS AND STRUCTURE OF ANATASE TiO2 (101) SURFACE

A systematic study of unrelaxed and relaxed surface characters on the TiO2 (101) surface has been carried out by first-principles calculations using plane-wave pseudopotential method. We find that O2c atoms have an inward relaxation of 0.012 Å and Ti5c atoms have an outward relaxation of 0.155 Å by taking a 24-layer slab with 5 Å vacuum width to consider the atomic relaxations, in good agreement with other theoretical values. The slab thickness has significant effect on the quality of band structure and density of states, and 24-layer slab is sufficient to present the electronic properties of TiO2 (101) surface. Atomic relaxations result in a large transfer of surface charges from outermost layer to inner layer, and the surface bonds have a rehybridization, which makes the ionization reduce and the covalence increase; we believe that it causes the surface bond shorten. A fine analysis of band structure and density of states of the TiO2 (101) surface shows that the surface relaxation induces the transformation from semi-metallic to semiconducting characteristic.