  To study digital Mott insulator LaTiO3 and band insulator SrTiO3 interfaces,
we apply correlated band theory (LDA+U) to (n,m) multilayers, 1<n,m<9. If the
on-site repulsion on Ti is large enough to model the magnetic insulating
behavior of cubic bulk LaTiO3, the charge imbalance at the interface is found
in all cases to be accommodated by disproportionation (Ti4+ + Ti3+), charge
ordering, and Ti3+ d_xy-orbital ordering, with antiferromagnetic exchange
coupling between the spins in the interface layer. Lattice relaxation affects
the conduction behavior by shifting (slightly but importantly) the lower
Hubbard band, but the disproportionation and orbital ordering are robust
against relaxation.
