  Electronic and magnetic structures of the newly synthesized cobalt
oxyselenide La2Co2Se2O3 (structurally similar to the superconducting iron
pnictides) are studied through density functional calculations. The obtained
results show that this material is a Mott insulator, and that it has a very
stable Co2+ high-spin ground state with a t2g-like orbital ordering, which is
substantiated by the calculated crystal-field excitation energies. The square
lattice of the Co2+ spins is found to have a strong antiferro (a weak ferro)
magnetic coupling for the second nearest neighbors (2nn) via O (Se2) and an
intermediate antiferro one for the 1nn, with the strength ratio about 10:1:3.
The present results account for the available experimental data of magnetism,
and the prediction of a planar frustrated (2x2) antiferromagnetic structure
would motivate a new experiment.
