  We address the electronic structure of quantum wells in polar-nonpolar oxide
heterojunction systems focusing on the case of non-polar BaVO$_3$ wells
surrounded by polar LaTiO$_3$ barriers. Our discussion is based on a density
functional description using the local spin density approximation with local
correlation corrections (LSDA+U). We conclude that a variety of quite different
two-dimensional electron systems can occur at interfaces between insulating
materials depending on band line-ups and on the geometrical arrangement of
polarity discontinuities.
