Calculation of the Φ-Ψ maps for alanyl and glycyl dipeptides with different additive and non-additive molecular mechanical models

Conformational energies are calculated for the glycyl and alanyl dipeptides using four different molecular mechanical models: (1) the Cornell et al. additive force field with Φ and Ψ dihedral parameters Vn/2 set to 0; (2) the standard Cornell et al. additive force field; (3) an alternative version of (2) with Φ and Ψ parameters optimized to fit high level ab initio energies calculated for all-αr and all-β alanine tetrapeptides; and 4) a non-additive variation of (1) which includes atom-centered charge polarization. Molecular mechanical energies are calculated with each model for low energy conformations of glycyl and alanyl dipeptides and compared with high level ab initio calculations. In addition, Φ-Ψ maps are calculated and plotted for all four models and compared.