The mechanism for the conversion of the 13/4 helix into the 4/1 helix of poly(alpha-isobutyl beta-L-aspartate) was simulated at the atomic level. A computational procedure based on a potential of mean force capable of creating multiple conformation states compatible with a given helical symmetry was used. Intermediate helical arrangements differing in 0.1 residues/turn were modeled and energetically evaluated to delineate the reaction coordinate. The conversion was found to proceed through poorly defined hydrogen bonded structures having an energy surplus of about 6 kcal/mol.residue. Results were consistent with experimental data and helpful for understanding fundamental aspects of the transition as it is observed in the solid state.