To directly evaluate the accuracy of the NNPs with respect to the reference DFT level for the same type of simulations performed in this work, Figure compares the relative energies of several Ge distributions and contents in UTL calculated using both the NNP and the DFT (PBE-D3(BJ)) geometry optimizations. The relative energies are given with respect to the lowest energy configuration obtained for the respective Ge concentration (1 to 8 Ge atoms per 38 T-sites unit cell). We found a very good agreement between the NNP and DFT calculated energies (MAE of 2.2 kJ/mol and RMSE of 3.1 kJ/mol), with Pearson correlation coefficients 36 ranging from 0.77 to 0.94. All structures used for error evaluation, including DFT and NNP calculated energies and forces, are available under: .