Ab Initio Calculations Versus Polarized Neutron Diffraction for the Spin Density of Free Radicals

The determination of the magnetization distribution using polarized neutron diffraction has played a key role during the last twenty years in the field of molecular magnetism. This distribution can also be obtained by first principle ab initio calculations. Such calculations always rely on approximations and the question that arises is to know whether the obtained results are reliable enough to represent accurately the properties of these molecules. The comparison between polarized neutron experimental results and ab initio calculations has turned to provide stringent tests for these methods. In the present article a comparison between experimental and theoretical results is made and is illustrated by examples based on magnetic free radicals.