As in previous work, initial weights were set to w F = 1.0 kcal mol 1 Å, w E = 0.3 kcal mol 1 , and w = 100.0 kcal mol 1 Å 3 . Models contained 1-through 4-body interactions, with corresponding polynomial orders of O 2b = 25, O 3b = 10, and O 4b = 4. Remaining hyperparameters for the fits were selected using previously described ChIMES heuristic approaches and are given in Table . All ChIMES simulations were run using either the ChIMES_MD code available in the CHIMES_LSQ repository, 8 or via LAMMPS 67 through the ChIMES_Calculator Library. Simulations used a 0.2 fs time step and were run for up to 100 ps, however all analysis was performed on only the first 5 ps to enable consistent comparison with DFT. Additional details on use of these tools is provided in Supplementary Information Section I.