A theoretical investigation was made of the possibility of ferromagnetism being induced by cation vacancies in non-magnetic oxides. A single Ca vacancy, VCa0, had a magnetic moment due to its open-shell structure, but the ferromagnetic interaction between 2 vacancies extended only to 4, or fewer, neighbors. In order to achieve magnetic percolation on a face-centered cubic lattice, with such a limited interaction range, a minimum of 4.9% vacancies, or a concentration 1.8 x 1021/cm3, was required. Total-energy calculations for CaO showed that, due to the high vacancy formation energy, it was not possible to obtain more than 0.003% or 1018/cm3 vacancies at equilibrium; even under the most favorable growth conditions. This showed that a non-equilibrium vacancy enhancement factor of 103 was required in order to produce magnetism in such systems.Magnetism without Magnetic Ions: Percolation, Exchange, and Formation Energies of Magnetism-Promoting Intrinsic Defects in CaO. J.Osorio-Guillén, S.Lany, S.V.Barabash, A.Zunger: Physical Review Letters, 2006, 96[10], 107203 (3pp)