  One of the main roadblocks that still hampers the practical use of molecular
nanomagnets is their cryogenic working temperature. In the pursuit of rational
strategies to design new molecular nanomagnets with increasing blocking
temperature, ab initio methodologies play an important role by guiding
synthetic efforts at the lab stage. Nevertheless, when evaluating
vibration-induced spin relaxation, these methodologies are still far from being
computationally fast enough to provide a useful predictive framework. Herein,
we present an inexpensive first-principles method devoted to evaluating
vibration-induced spin relaxation in molecular f-block single-ion magnets, with
the important advantage of requiring only one CASSCF calculation. We use a case
study to illustrate the method, and propose chemical modifications in the
ligand environment with the aim of suppressing spin relaxation.
