  Using density functional theory within the LSDA + U method, we investigate
the effect of strain on the spin state and magnetic ordering in perovskite
lanthanum cobaltite, LaCoO3. We show that, while strain-induced changes in
lattice parameters are insufficient to stabilize a non-zero spin state,
additional heteroepitaxial symmetry constraints -- in particular the
suppression of octahedral rotations -- stabilize a ferromagnetic
intermediate-spin state. By comparing with experimental data for the bulk
material, we calculate an upper bound on the Hubbard U value, and describe the
role that the on-site Coulomb interaction plays in determining the spin-state
configuration.
