Structural distortion and charge redistribution in SrTiO3 (111) polar surfaces

The structural and electronic properties of the SrTiO3 (111) polar surfaces are studied using first-principles calculations. The structural distortions for Ti termination are larger than that for SrO3 termination. A negative charge density of −0.55e is concentrated at the surface of Ti termination, which may explain the recent finding of two-dimensional electron gas exits at the SrTiO3 (111) surface. A positive charge density of 0.64e is accumulated at the surface of SrO3 termination. The nonstoichiometric TiO and SrO2 terminations are also considered. Oxygen octahedrons tilt to the opposite direction in the adjacent cells along the stacking direction. TiO and SrO2 terminated slabs are both insulating with surface charge modified relatively small. The surface energies for all the SrTiO3 (001), (011) and (111) surfaces are calculated to compare the surface stability.