  Tricobalt tetraoxide (Co3O4) is an important catalyst and Co3O4(110) is a
frequently exposed surface in Co3O4 nanomaterials. We employed
Density-functional theory with on-site Coulomb repulsion U term to study the
atomic structures, energetics, magnetic and electronic properties of the two
possible terminations, A and B, of this surface. These calculations predict A
as the stable termination in a wide range of oxygen chemical potentials,
consistent with recent experimental observations. The Co3+ ions do not have a
magnetic moment in the bulk, but become magnetic at the surface, which leads to
surface magnetic orderings different from the one in the bulk. Surface
electronic states are present in the lower half of the bulk band gap and cause
partial metallization of both surface terminations. These states are
responsible for the charge compensation mechanism stabilizing both polar
terminations. The computed critical thickness for polarity compensation is 4
layers.
