... the scope of the HF method and if the presence of unknown groups makeapplication of specifically parame terized force fields impossible, a rule-based forcefield is preferable to a semiempirical ... this group is a single force field, the newly im-plemented OPLS_AA force field, with a performance probably worse than B3LYP(MAE = 0.75 kcal/mol).It is significant that the group of force fields ... conformational energies is 0.49 kcal/mol for B3LYP, 0.66 kcal/mol for HF, and 1.37 kcal/mol for PM3. We can say with 98%confidence that B3LYP is more accurate than HF for this type of comparison,...