  We present first-principles total-energy calculations of (001) surfaces of
SrTiO3. Both SrO-terminated and TiO2-terminated surfaces are considered, and
the results are compared with previous calculations for BaTiO3 surfaces. The
major differences are in the details of the relaxed surface structures. Our
calculations argue against the existence of a large ferroelectric relaxation in
the surface layer, as had been previously proposed. We do find some indications
of a weak surface ferroelectric instability, but so weak as to be easily
destroyed by thermal fluctuations except perhaps at quite low temperatures. We
also compute surface relaxation energies and surface electronic band
structures, obtaining results that are generally similar to those for BaTiO3.
