  Recent works suggest that the surface chemistry, in particular, the presence
of oxygen vacancies can affect the polarization in a ferroelectric material.
This should, in turn, influence the domain ordering driven by the need to
screen the depolarizing field. Here we show using density functional theory
that the presence of oxygen vacancies at the surface of BaTiO3 (001)
preferentially stabilizes an inward pointing, P-, polarization. Mirror electron
microscopy measurements of the domain ordering confirm the theoretical results.
