Density-functional calculations are used to study the electronic and magnetic structures of Ca 2 RuO 4 . It is found that the magnetic and structural degrees of freedom are strongly coupled. It is also found that the electronic structure near the Fermi level is described by the antibonding Ru 4d and O 2p bands as is the case for other 4d Ruddlesden-Popper materials. The distortion of the lattice has a pronounced effect on the magnetic ordering and localization of the carriers. The calculations

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... ive a good estimate of the magnetic moment and they indicate that there is a magnetic instability in this compound.