One of the primary tasks of fitting an MLIP is to collect appropriate structures for the reference database, which determines the domain of applicability of the model. For example, some successful MLIPs in materials modelling are fitted to relatively small unit cells containing tens of atoms, enabling molecular dynamics simulations of up to a hundred thousand atoms for a few nanoseconds. The situation is equivalent for MLIPs for small organic molecules, where the chemical space of potential compounds is too vast for the training set to encompass every possible compound. Therefore, MLIPs based on local environments are expected to extrapolate to novel chemical entities if the training database contains a sufficient number of atomic environments that are similar to those in the new compound.