First-principles investigation of stability and structural properties of the BaTiO₃ (110) polar surface

The atomic and electronic structures of the BaTiO₃ (110) polar surface were systematically investigated by first-principles density functional theory (DFT) calculations with use of slab models. The relaxations and rumplings of five different (1 × 1) terminations were considered. According to the results of the charge redistribution, the polarity compensation conditions can be achieved in both stoichiometric and nonstoichiometric terminations, but their compensation mechanisms are obviously different. For the BaTiO and O ₂ stoichiometric terminations, the intensive electronic structure changes with respect to the bulk crystal result in larger structural distortions and cleavage energies than the nonstoichiometric ones. For the TiO, Ba, and O nonstoichiometric terminations, whose electronic structures are qualitatively similar to that of the bulk crystal, their insulating characteristics are retained because no filling of surface states was found. Furthermore, the computation results of the surface grand potentials (SGPs), which were used to distinguish the relative stabilities of different terminations, clearly suggest the existence of four distinct stable (110) terminations, in which the BaTiO stoichiometric termination can only exist in a small region with O-poor condition.