The alternative definition was to generate 10 binned histograms out of the values of quantum properties of molecules containing specific atom pair, divided by the number of occurrences of the atom pair. As a result, 110 different values were assigned to atom pairs. The nature of modified atom pairs makes them highly dependent on the composition of the quantum properties database which impacts the applicability domain of QAP. Due to the narrow group of elements present in the QM9-extended-plus database, atom pairs are limited to C, O, N, F, S, Cl, and Br elements. The limitation transfers to the applicability domain. In the research molecules containing only atom pairs from the set generated from the QM9-extended-plus database were curated from experimental databases.