Ab initio calculations of the atomic and electronic structure of CaTiO3 (001) and (011) surfaces

TL;DR

This study uses ab initio calculations to analyze the atomic structure, relaxations, and surface energies of CaTiO3 surfaces, revealing significant differences between surface terminations and a notable increase in Ti-O covalency at the (011) surface.

Contribution

It provides detailed ab initio insights into the relaxations, energetics, and bonding of CaTiO3 surfaces, highlighting differences from previous models and emphasizing increased covalency at the (011) surface.

Findings

All upper-layer atoms relax inwards on CaO-terminated (001) surface.

Surface energies are similar for CaO and TiO2 terminations of (001).

Different terminations of (011) surface have markedly different energies.

Abstract

We present the results of calculations of surface relaxations, energetics, and bonding properties for CaTiO3 (001) and (011) surfaces using a hybrid B3PW description of exchange and correlation. We consider both CaO and TiO2 terminations of the non-polar (001) surface, and Ca, TiO and O terminations of the polar (011) surface. On the (001) surfaces, we find that all upper-layer atoms relax inwards on the CaO-terminated surface, while outward relaxations of all atoms in the second layer are found for both terminations. For the TiO2-terminated (001) surface, the largest relaxations are on the second-layer atoms. The surface rumpling is much larger for the CaO-terminated than for the TiO2-terminated (001) surface, but their surface energies are quite similar at 0.94eV and 1.13eV respectively. In contrast, different terminations of the (011) CaTiO3 surface lead to very different surface energies of 1.86eV, 1.91eV, and 3.13eV for the O-terminated, Ca-terminated, and TiO-terminated (011) surface respectively. Our results for surface energies contrast sharply with those of Zhang et al. [Phys. Rev. B 76, 115426 (2007)], where the authors found a rather different pattern of surface energies. We predict a considerable increase of the Ti-O chemical bond covalency near the (011) surface as compared both to the bulk and to the (001) surface.