We note that using LibTorch was essential to the performance and scaling of the ML/MM (MBIS charges with polarization) coupling mode. Specifically, a direct serial implementation of the charge gradient with respect to positions performs poorly unless extra care is taken in order to discard the terms that correspond to ML atoms lying further away than the model's cutoff, which is challenging to do given Sander's QM/MM interface. We also provide, for reference purposes, the direct serial implementation, which was used to validate our LibTorch implementation.