Ab initio calculations for the polar (0 0 1) surfaces of YAlO3

The results of ab initio calculations of polar YAlO3 (0 0 1) surfaces by means of a hybrid B3LYP exchange-correlation functional as it is implemented in the CRYSTAL computer code are presented. Both polar YO and AlO2-terminations of the cubic YAlO3 (0 0 1) surface were considered. We performed relaxation of atoms on the upper three layers of both YO and AlO2-terminated YAlO3 (0 0 1) surfaces using in our calculations slabs containing 22 and 23 atoms as well as 9 layers, respectively. We predict a significant increase of the Al-O chemical bond covalency on the AlO2-terminated YAlO3 (0 0 1) surface with respect to the YAlO3 bulk. Our calculated YO and AlO2-terminated YAlO3 polar (0 0 1) surface energies are considerably larger than the related structure ABO3 perovskite neutral (0 0 1) surface energies, but comparable with ABO3 perovskite polar (0 1 1) surface energies. Our calculated optical band gap near the YO-terminated YAlO3 (0 0 1) surface is decreased, but near the AlO2-terminated (0 0 1) surface is increased with respect to the calculated YAlO3 bulk optical band gap.