  We interpret via advanced ab initio calculations the multiple phase
transitions observed recently in ultra-thin LaNiO$_{3}$/LaAlO$_{3}$
superlattices. The ground state is insulating, charge-ordered, and
antiferromagnetic due to concurrent structural distortion and weak valency
disproportionation. We infer distinct transitions at 40 K and 150 K,
respectively, from antiferromagnetic order to moment disorder, and from
structurally-dimerized insulator to an undistorted metallic Pauli paramagnet
(exhibiting a cuprate-like Fermi surface). The results are in satisfactory
agreement with experiment.
