Ab initio calculations of the (111) polar surfaces

The stoichiometric terminations and nonstoichiometric terminations have been constructed for CaTiO3 (111) surface. The cleavage and surface energies, surface grand potential and surface electronic structure have been calculated for the two main classes of terminations using ab initio plane wave ultrasoft pseudopotential method based on Local Density Approximation (LDA). The results show that the stoichiometric terminations are unstable compared with the nonstoichiometric terminations and the polarity compensation achieved through the modification of the surface stoichiometry is more effective than that by the anomalous filling of the surface states. In the O and Ca chemical environments, only CaO2 and TiO terminations can be formed; the CaO3 and Ti terminations cannot be stabilized, even in very O-rich chemical environment.