The LightGBM energies are then used to select molecules with a storage density of ≥0.40 kJ/g and a barrier height of ≥165 kJ/mol (the PM3 barrier for the parent system), of which there are 957,587. The highest storage density found in this set is 0.58 kJ/g so the main conclusion is that there are no molecules among the 230 billion molecules considered here with a storage density approaching 1 kJ/g. From these roughly 1 million molecules we need to select at most 50,000 molecules for SQM refinement. Figure shows an overview of the number of molecules with various ranges of barrier heights and storage densities. After much deliberation we chose two sets for SQM refinement. The first set is the 1969 molecules with barriers and storage densities of >165 kJ/mol and >0.50 kJ/g. Given the tendency of PM3 (and, hence, the LightGBM model) to overestimate the barrier height, these are almost certainly false positives but, given their high storage densities, we include them "just in case" The second set is the 33,085 molecules with barriers and storage densities of >185 kJ/mol and >0.45 kJ/g (Figure (b)), which, given the higher barriers, are more likely to include true positives.