It is worth noting that both the FIT and Williams potentials (at least as described in and respectively) characterized electrostatic interactions using multipoles derived from isolated-molecule quan-tum mechanical (QM) calculations. Therefore, strictly speaking, they should not be used in conjunction with other electrostatic descriptions (e.g., point-charges). Moreover, while the use of combining rules is convenient to manage the number of model parameters, there is no rigorous theoretical justification of their validity. More recent work has highlighted the importance of determining cross-interaction parameters explicitly, as well as providing parameterizations consistent with more modern electrostatic models . These parameterizations have shown notable improvements for both energetic and geometric predictions of experimental crystal structure. Finally, in these modern methods, parameterization has also shifted towards minimising geometric and energetic discrepancies of the relaxed crystal geometries relative to the reference structures. Whilst this significantly increases the complexity of the parameter estimation procedure, it is theoretically more robust than the earlier approaches. Since any experimentally-observed reference structures must also be a local minimum on the lattice energy landscape, matching geometry and energy specifically at the relaxed crystal structure strictly enforces this local optimality criterion. In contrast, the FIT and Williams parameterizations only loosely compel optimality by minimising forces at the experimental geometry.