To quantitatively estimate lattice free energies, we build and expand on our earlier work , where we identified several useful heuristics for applying reweighted PGMs to obtain accurate free energy estimates. The only MD data that is required for training and reweighting the PGMs is that which is sampled in the physical macrostates of interest. This approach, therefore, entirely avoids sampling multiple intermediate Hamiltonians (details provided in the Simulations Setup section), typical of free energy perturbation methods such as the Einstein Crystal . In Ref. , we used isolated small molecules in a vacuum as representative case studies, with 3N -9 out of 3N -6 of the relevant intramolecular degrees of freedom (DOFs) represented using internal coordinates . Those PGMs relied on a mixed coordinate representation of the given molecule. Specifically, we kept three of the atoms represented in Cartesian coordinates to serve as a starting point for a bijective reconstruction of all remaining atoms of the molecule from the internal coordinates. We referred to these three Cartesian atoms as the Cartesian block. When dealing with isolated molecules in a vacuum, the Cartesian block only has three relevant DOFs. However, in systems containing more than one molecule, like crystal supercells, all nine DOFs of the Cartesian block of each molecule must be jointly modeled by the PGM.