In a molecule, each rotatable bond, as identified by a chosen definition, can be associated with a distinct torsion profile. These torsion profiles are influenced by the molecule's overall structure, giving each dihedral an individual profile. Though each torsion is, in principle, unique, it is possible to assign them to a comparatively small number of archetypes, as for instance introduced by Schärfer et al. and Guba et al. . The ETKDG conformer generation algorithm builds upon this work, using a hierarchy of torsion angles that are matched via SMARTS patterns with small-molecule crystallographic data from the Cambridge Structural Database (CSD) . Each torsion angle distribution obtained from the CSD was fitted by describing the torsion energies with a Fourier series as commonly used in classical force fields ,