  Orbital reconstruction at interfaces between YBa2Cu3O6 and SrO-terminated
SrTiO3 is studied using local spin density approximation (LSDA) with
intra-atomic Coulomb repulsion (LSDA+U). The change of population of
interfacial Cu 3d orbitals results in stabilization of a new oxidation state
$3d^8$ which involves an additional modification of orbital occupancies in the
nearest SrO and TiO2 layers. We find that an increase of electron charge in Cu
3d_{x^2-y^2} states counterbalances a depopulation of 3d_{3z^2-r^2} orbitals
which induces, on account of the onsite Coulomb repulsion U, a splitting of
3d_{3z^2-r^2} states at CuO2-SrO interfaces.
