These simple electrostatics arguments were also successfully translated into a more quantitative classical electrostatics repulsion energy minimization procedure, which showed to be capable of semi-quantitatively predicting the specific direction of the magnetic anisotropy axis in many Dy(III) single-molecule magnets. Despite these useful results, it is known since the 1950s that quantitative descriptions of lanthanide-ligand bonding cannot be achieved without accounting for non-covalent interactions other than pure electrostatics (e.g induction, contact or dispersion interactions), and for various flavours of so-called covalent contributions (charge transfer excitations of various kinds). . A way to systematically account for all possible metal-ligand electronic interactions consists of ab initio calculations, typically based on molecular orbital (MO) theory, which in recent years have proved to be a reliable tool for the description of low-lying multiplets of lanthanide complexes with good accuracy . However, in these methods the interactions between the electrons in the environment and the ion are not treated in a perturbative manner, leading not only to an increased computational cost, but also to a difficult interpretation of the different physical mechanisms involved in the description of metal-ligand bonding.