Defect-free $\mathrm{Ca}\mathrm{Ti}{\mathrm{O}}_3$ is a band insulator, but angle-resolved photoemission spectroscopy experiments have demonstrated the existence of a nanometer-thin two-dimensional electron system (2DES) at the (001)-oriented surface of this compound. Our ab initio study finds that while oxygen defects are the driving mechanism for the metallicity, tiltings and rotations of the oxygen octahedra significantly impact the electronic structure of the 2DES and its response to externally applied strain deformations. The low-energy conduction subbands have a mixed $t_{2g}\text{−}{e}_g$ orbital character close to the center of the Brillouin zone. Good agreement with the experimental spectra is found for $\mathrm{Ti}{\mathrm{O}}_2$ surface divacancy configurations.

• Received 28 June 2022
• Revised 10 November 2022
• Accepted 21 December 2022

DOI:https://doi.org/10.1103/PhysRevB.107.045101