The atomic geometry of a TiO2(110) surface upon creation of an O defect site and formation of a hydroxyl group was investigated using 3x1, 2x2 super-cells by spin polarized density functional theory calculations. It was found that both the removal of a bridging O atom and the formation of an OH group lead to distortion in the atomic positions of the neighboring atoms depending on the choice of the unit cell used in the calculations. The scanning tunnelling microscopy simulations performed using the 2x2 unit cell suggested that both an O vacancy and a hydroxyl group should be observed experimentally as a bright protrusion but of different shapes. The O vacancy exhibits a spherical shape whereas the OH group was elongated perpendicular to the [001] direction. In contrast, in the 3x1 super-cell, the OH group appeared as a bright spot while the O defect looked darker. These findings clearly suggested that a proper geometry was necessary to reproduce experimental scanning tunneling microscopic images of an O vacancy and a hydroxyl group on a TiO2(110) surface.

Atomic Geometry and STM Simulations of a TiO2(110) Surface Upon Formation of an Oxygen Vacancy and a Hydroxyl Group. Mutombo, P., Kiss, A.M., Berkó, A., Cháb, V.: Modelling and Simulation in Materials Science and Engineering, 2008, 16[2], 025007