Theoretical modelling of the energy surface (001) and topology of CaZrO₃ perovskite

I present the results of ab initio calculations of surface relaxations, rumplings, energetics, optical band gaps, and charge distribution for the CaZrO₃ (001) surfaces using computer code CRYSTAL and a hybrid description of exchange and correlation. I consider both CaO and ZrO₂-terminations of the CaZrO₃ (001) surface. On the both CaO and ZrO₂-terminated CaZrO₃ (001) surfaces, I find that all upper and third layer atoms relax inwards, whereas all second layer atoms relax upwards. I predict a considerable increase of the Zr-O chemical bond covalency (0.102e) near the ZrO₂-terminated CaZrO₃ (001) surface relative to the CaZrO₃ bulk (0.086e). My calculated CaO (0.87 eV) and ZrO₂-terminated (1.33 eV) CaZrO₃ (001) surface energies are considerably smaller than another ABO₃ perovskite polar (011) and (111) surface energies. The calculated optical band gaps near the CaO (5.00 eV) and ZrO₂-terminated (5.22 eV) CaZrO3 (001) surfaces are considerably reduced with respect to the bulk band gap (5.40 eV).