Effect of relaxation on structure and reactivity of anatase (1 0 0) and (0 0 1) surfaces

The effect of relaxation on the anatase (1 0 0) and (0 0 1) surfaces has been investigated by first-principles periodic calculations. The (1 0 0) surface is thermodynamically less stable and presents important relaxations of the surface atoms belonging to the external layers. Relaxation of two layers seems to be necessary to obtain a good description of the surface. The (0 0 1) surface is more stable and shows a breaking of the symmetry upon relaxation. We report geometrical parameters and the projected density of states for the two surfaces. Finally, the effect of relaxation has been studied for the adsorption of hydrogen on the two slabs. On the (1 0 0) plane adsorption energy decreases with the degree of relaxation, while on the (0 0 1) plane the effect is the opposite.