  First-principles total-energy calculations are carried out for (001) surfaces
of the cubic perovskite ATiO3 compounds PbTiO3, BaTiO3, and SrTiO3. Both
AO-terminated and TiO2-terminated surfaces are considered, and fully-relaxed
atomic configurations are determined. In general, BaTiO3 and SrTiO3 are found
to have a rather similar behavior, while PbTiO3 is different in many respects
because of the partially covalent character of the Pb-O bonds. PbTiO3 and
BaTiO3 are ferroelectrics, and the influence of the surface upon the
ferroelectric distortions is studied for the case of a tetragonal ferroelectric
distortion parallel to the surface. The surface relaxation energies are found
to be substantial, i.e., many times larger than the bulk ferroelectric well
depth. Nevertheless, the influence of the surface upon the ferroelectric order
parameter is modest, and is qualitatively as well as quantitatively different
for the two materials. Surface energies and electronic properties are also
computed. It is found that for BaTiO3 and SrTiO3 surfaces, both AO-terminated
and TiO2-terminated surfaces can be thermodynamically stable, whereas for
PbTiO3 only the PbO surface termination is stable.
