Mean absolute error force field

Fig. 2 summarizes the overall results obtained by the different force fields and for different structural classes of compounds in terms of mean absolute errors. The performance of the force fields for particular classes of compounds is discussed in the following sections. Fig. 2 also includes the overall results for three QM methods (PM3, FIF/6-31G and B3LYP/6-31G ). These results will be discussed in Sec. 4. 

Figure 2 Comparison of mean absolute errors (in kcal/mol) for different structural classes of organic compounds obtained in calculations of conformational energy differences by using different commonly used force fields.

Qui et al. have compared experimental and calculated hydration free energies for a set of 35 small organic molecules with diverse functional groups by using the OPLS force field and the GB/SA hydration model [57], These calculations resulted in a mean absolute error of 0.9 kcal/mol. It is of interest to note that the results obtained with the GB/SA model were very similar to those obtained by the corresponding calculations using the full Poisson-Boltzmann equation. 

Figure 8 Comparison of mean absolute errors in force field calculations on conformational energy differences for organic molecules of different structural classes. (Compiled from the results reported in Refs. 25 and 27.)...

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