Ab Initio Computations of O and AO as well as ReO2, WO2 and BO2-Terminated ReO3, WO3, BaTiO3, SrTiO3 and BaZrO3 (001) Surfaces

We present and discuss the results of surface relaxation and rumpling computations for ReO₃, WO₃, SrTiO₃, BaTiO₃ and BaZrO₃ (001) surfaces employing a hybrid B3LYP or B3PW description of exchange and correlation. In particular, we perform the first B3LYP computations for O-terminated ReO₃ and WO₃ (001) surfaces. In most cases, according to our B3LYP or B3PW computations for both surface terminations BO₂-and O, AO-terminated ReO₃, WO₃, BaTiO₃, SrTiO₃ and BaZrO₃ (001) surface upper layer atoms shift downwards, towards the bulk, the second layer atoms shift upwards and the third layer atoms, again, shift downwards. Our ab initio computes that ReO₃, WO₃, BaTiO₃, SrTiO₃ and BaZrO₃ (001) surface Γ-Γ bandgaps are always smaller than their respective bulk Γ-Γ bandgaps. Our first principles compute that B-O atom chemical bond populations in the BaTiO₃, SrTiO₃ and BaZrO₃ perovskite bulk are always smaller than near their BO₂-terminated (001) surfaces. Just opposite, the Re-O and W-O chemical bond populations in the ReO₃ (0.212e) and WO₃ (0.142e) bulk are slightly larger than near the ReO₂ and WO₂-terminated ReO₃ as well as WO₃ (001) surfaces (0.170e and 0.108e, respectively).