  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.
