| Abstract
| - The performance of the complete active space second-order perturbation theory (CASPT2) to accurately predictmagnetic coupling in a wide series of molecules and solid state compounds has been established. It is shownthat CASPT2, based on a reference wave function that only includes the effects described by the Andersonor Hay−Thibeault−Hoffmann model, correctly reproduces all experimental trends. For a complete quantitativeagreement with experiment (or with accurate results arising from the difference dedicated configurationinteraction method), it is necessary to include effects that go beyond the Anderson model in the referencewave function. The CASPT2 method is computationally less demanding than CI based methods and, hence,allows us to extend the study of magnetic coupling parameters to larger molecules or systems with elevatedspin moments. Moreover, CASPT2 provides a reliable and accurate alternative to density functional basedmethods that require the use of a broken symmetry approach.
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