  We present the results of first-principles calculations on two possible
terminations of the (001) surfaces of SrTiO3 (STO), BaTiO3 (BTO), and PbTiO3
(PTO) perovskite crystals. Atomic structure and the electronic configurations
were calculated for different 2D slabs, both stoichiometric and
non-stoichiometric, using hybrid (B3PW) exchange-correlation technique and
reoptimized basis sets of atomic (Gaussian) orbitals. Results are compared with
previous calculations and available experimental data. The electronic density
distribution near the surface and covalency effects are discussed in details
for all three perovskites.
