Ab initio computations of BaZrO3, CaTiO3, SrTiO3 perovskite as well as WO3 and ReO3 (001) surfaces

We computed, at the ab initio level, BaZrO3, CaTiO3, SrTiO3 as well as WO3 and ReO3 (001) surfaces and analyzed systematic tendencies therein. As obtained by our ab initio hybrid DFT-HF computations, at BO2-terminated (001) surfaces of investigated ABO3 perovskites as well as WO3 and ReO3 oxides, all top-layer ions shift in the direction of the crystal bulk. The single-deviation from this tendency is upward shift of the WO2-terminated WO3 (001) surface top layer O ion by the magnitude of +0.42% of the bulk lattice constant a0. In contrary, all second layer ions, with the single exception of ReO2-terminated ReO3 (001) surface O ion, shifts upwards. Our computed BO2-terminated SrTiO3, CaTiO3, BaZrO3, WO3 and ReO3 (001) surface Γ–Γ band gaps always are smaller than their respective bulk Γ–Γ band gaps. The B–O ion chemical bond populations in the SrTiO3, CaTiO3 and BaZrO3 perovskite bulk are always smaller than at their nearby BO2-terminated (001) surfaces. On the contrary, the W–O and Re–O ion chemical bond populations in the WO3 (0.142e) and ReO3 (0.212e) bulk are slightly larger than at nearby the WO2- and ReO2-terminated WO3 and ReO3 (001) surfaces (0.108e and 0.170e). Nonetheless, the W–O and Re–O chemical bond populations between the W and Re ions located in the upper layer and the O ions located in the second layer of the WO2- and ReO2-terminated (001) surfaces (0.278e and 0.262e) are the absolutely largest bond populations in the WO3 and ReO3 crystals.