As previously discussed, the multiple natural Lewis structures encountered within the tetrazole dataset (Figure ) prompted us to construct additional NBO parameters. Due to the aromaticity of tetrazoles, we started by constructing minima, maxima, sums, and averages of NBO orbital occupancies, energies, bond orders, and energy gaps for the calculated localized π NBOs. Importantly, multiple Lewis structures were unified by identifying NBOs that are related by resonance. For instance, the natural Lewis structure of some tetrazoles contained an N 2 =N 3 double bond ("charged" NBO structures) whereas in the majority of tetrazoles it is localized as a N 1 =N 2 double bond ("uncharged" NBO structures). Hence, these π orbitals were treated as a single structural feature for the design of additional descriptors. Closer inspection of the σ NBO energies and orbital occupancies of tetrazoles with "charged" NBO structures revealed systemic alterations based on the calculated Lewis structure of the tetrazole. Analogous feature engineering was thus also performed on σ NBO orbitals. Taken together, these improvements offered a more uniform description of the π-system and the σ skeleton of tetrazoles in a manner agnostic of their Lewis structures.