A Ternary Reconstruction on the SrTiO₃(001) Surface

We revisit the well-studied 2 × 1 SrTiO₃(001) surface, long presumed to adopt a double-layer TiO₂ reconstruction, and propose a fundamentally new structural model. By combining evolutionary algorithms for global optimization, density-functional theory calculations, and experimental insights, we uncover a ternary surface reconstruction that exhibits substantially lower surface energy under typical experimental conditions compared to previously proposed models. This newly identified structure aligns closely with high-resolution electron microscopy (HREM) observations and explains the experimentally observed Sr precipitation on the surface. Moreover, it can be extended to the BaTiO₃(001) surface, suggesting broader implications for similar perovskite systems. Our findings challenge the prevailing understanding of this surface and offer a fresh perspective that may reshape interpretations of surface properties and interactions in perovskite oxides.