Magnetic coupling in biradicals, binuclear complexes and wide-gap insulators: a survey of ab initio wave function and density functional theory approaches

State-of-the-art computational approaches to magnetic coupling in biradicals, dinuclear complexes and wide-gap insulators are reviewed with the aim to provide a unified point of view. The most rigorous wavefunction-based methods provide an accurate description of magnetic coupling in all these systems, whereas density-functional-based methods within the broken symmetry approach provide an alternative, yet efficient, computational tool. The use of mapping procedures permits the broken symmetry solution to be related to the appropriate spin state. Different arguments are given to show that the neglect of this procedure may lead to values in agreement with experiment, but at the cost of serious contradictions.