Rare earth elements are prized for their uses in magnetic and optical applications. Central to these utilities are the spin dynamics of the strongly-correlated 4f electrons. Understanding how spins interact with their environment underpins their behaviours, but these effects are usually difficult to detect directly. As such, theoretical approaches that calculate spin interactions are central to modelling spectroscopic and magnetic responses that can be used to infer the underlying dynamics. We have recently developed accurate tools for predicting the spin dynamics of rare earth molecular materials, including vibronic spectroscopy, magnetic hysteresis and solution phase paramagnetic NMR effects. This talk will outline some of these latest advances.