  Motivated by recent Fermi surface and transport measurements on LaNiO3, we
study the Mott Metal-Insulator transitions of perovskite nickelates, with the
chemical formula RNiO3, where R is a rare-earth ion. We introduce and study a
minimal two-band model, which takes into account only the eg bands. In the weak
to intermediate correlation limit, a Hartree-Fock analysis predicts charge and
spin order consistent with experiments on R=Pr, Nd, driven by Fermi surface
nesting. It also produces an interesting semi-metallic electronic state in the
model when an ideal cubic structure is assumed. We also study the model in the
strong interaction limit, and find that the charge and magnetic order observed
in experiment exist only in the presence of very large Hund's coupling,
suggesting that additional physics is required to explain the properties of the
more insulating nickelates, R=Eu,Lu,Y. Next, we extend our analysis to slabs of
finite thickness. In ultra-thin slabs, quantum confinement effects
substantially change the nesting properties and the magnetic ordering of the
bulk, driving the material to exhibit highly anisotropic transport properties.
However, pure confinement alone does not significantly enhance insulating
behavior. Based on these results, we discuss the importance of various physical
effects, and propose some experiments.
