The latter is defined in terms of topologically equivalent atoms, meaning they have identical environments in terms of connectivity: they are connected to the same number and type of atoms, and those atoms themselves exhibit the same connectivity in a recursive manner. This equivalence arises from the symmetry of the labeled molecular graph, a graph-theoretical representation of the molecule. Dependencies between FF parameters stem from the chemical equivalence of atoms, which determines the atom types to which they are assigned. Typically, the number of data points is smaller than the number of parameters in the FF, resulting in many strongly correlated parameters. To enhance the stability of the fitting process and avoid over-fitting, equivalent force constants are not independently varied during parameterization. Additionally, the equilibrium values of equivalent FF terms are averaged to produce symmetrized values.