Can DFT calculations help the molecular designer to construct molecule based magnetic materials?

The use of small molecule density functional theory calculations to enhance and complement experimental work in the area of molecule-based magnetic materials is highlighted through a review of the author's own work. Focus is on the spin density of radicals and the consequences this have on the magnetic coupling between interacting spins in solid-state compounds. Both examples of the McConnell I mechanism, based on an analysis of possible orthogonality and sign of the interacting spins, and of the McConnell II mechanism based on charge transfer are encountered. It is concluded that such relatively small and easy calculations on the molecular 'bricks' can often help in the analysis of spin interactions in the resulting material. They can give direct indications of the McConnell I type of exchange interaction or they can give hints about possible pathways for the McConnell II mechanism. However, care should be taken not to over-interpret the results and one should be aware of the limitations of the methods.