Chemical Trends of Surface Reconstruction and Band Positions of Nonmetallic Perovskite Oxides from First Principles

Abstract

An evolutionary algorithm search in combination with first-principles calculations is performed to systematically predict the reconstructed surface structures of nonmetallic perovskite oxides. Four types of lowest-energy reconstruction patterns are obtained for the macroscopically stoichiometric (001) surfaces of NaTaO3, KTaO3, CaTiO3, SrTiO3, YAlO3, and LaAlO3 as representatives of A+B5+O3, A2+B4+O3, and A3+B3+O3 systems. We explain chemical trends in the surface energies and band positions of 10 perovskite oxides, additionally including KNbO3, BaTiO3, BaZrO3, and LaGaO3, in terms of the atomic environments at the outermost reconstructed surface layers. Regaining A-O (B-O) coordination numbers and bond lengths at the surfaces is found to stabilize the A2+B4+O3 and A3+B3+O3 (A+B5+O3) surfaces. Decreasing the coordination number of cation A (B) leads to shallow (deep) valence band maxima and conduction band minima relative to the vacuum level. Our study provides general insights into the surface reconstruction and band alignment of nonmetallic perovskite oxides.