Overall, our results show that when considering isolated polypeptides, for the local-mode frequencies all three vibrational maps are in reasonable agreement with the reference values extracted from quantum-chemical calculations. For the Tokmakoff model, the correlation between predicted frequencies and the reference values is slightly worse, in particular for the polyalanine test cases. For all models, the performance is worse for the more realistic test cases that feature different amino acids than for the polyalanine models.