An additional decision to make is how many parameters should be used to parametrize a given torsional rotation? Rotatable bonds can have many torsion parameters associated with them, due to the number of unique combinations of atom quartets running through the central bond, and the overall torsional profile is given by the sum of these terms. Using a traditional atom-typed parameter assignment scheme can lead to insufficient flexibility. For example, for the highlighted rotation in aspirin, shown in Figure (right), atom typed schemes would use a single set of torsion parameters, corresponding to the GAFF atom types c-os-ca-ca.