AB-INITIO STUDY OF BATIO3 SURFACES

We have carried out first-principles total-energy calculations of (001 ) surfaces of the tetragonal and cubic phases of BaTiO3. Both BaO-term inated (type I) and TiO2-terminated (type II) surfaces are considered, and the atomic configurations have been fully relaxed. We found no de ep-gap surface states for any of the surfaces, in agreement with previ ous theoretical studies. However, the gap is reduced for the type-II s urface, especially in the cubic phase. The surface relaxation energies are found to be substantial, i.e., many times larger than the bulk fe rroelectric well depth. Nevertheless, the influence of the surface upo n the ferroelectric order parameter is modest; we find only a small en hancement of the ferroelectricity near the surface.