Ab initiomodeling ofCaTiO3(110) polar surfaces

The TiO, Ca, asymmetric A-type O-terminated and symmetric B-type O-terminated surfaces have been constructed for $\mathrm{Ca}\mathrm{Ti}{\mathrm{O}}_{3}$ (110) surface. The cleavage and surface energies, surface grand potential, surface relaxation, and surface electronic structure have been calculated for these polar terminations by using ab initio plane waves ultrasoft pseudopotential method based on generalized gradient approximation. The results show that the favorable $\mathrm{Ca}\mathrm{Ti}{\mathrm{O}}_{3}$ (110) and (001) surfaces are CaO-terminated (001) surface, A-type O-terminated (110) surface, and $\mathrm{Ti}{\mathrm{O}}_{2}$-terminated (001) surface successively, in view of the surface energy minimization. The Ca termination is stable in O- and Ca-rich environments, however, its complementary TiO termination is stable in O- and Ca-poor conditions. The A-type O termination shows a stability domain in moderate O and Ca environments. In the range of accessible values of $\ensuremath{\Delta}{\ensuremath{\mu}}_{\mathrm{O}}$, only Ca and A-type O-terminated surfaces are likely to be observed. Moreover, a large surface rumpling s of 12.10% $a$ is found for the TiO-terminated surface due to inward movement of Ti ion and outward movement of O ion. The surface band gaps for the relaxed TiO and A-type O terminations are larger than the bulk band gap; however, the values for Ca and B-type O terminations are smaller.