First, a molecular dynamic (MD) simulation was performed using Gromacs and the AMBER99SB-ILDN force field and the TIP3P water model . The padding of the cuboid water box around the peptide was set to 1 nm, resulting in simulation boxes containing 2000-4000 water molecules depending on the aspect ratio of the peptide. If necessary, the net charge was equalized by replacing one of the water molecules with a chloride anion. All structures were equilibrated at room temperature and standard pressure. As no restraints were applied to the initial idealized structures, and the polypeptides changed their conformations during the following MD runs. For the alanine α-helix only the first 2.5 ns of the trajectory were used for extracting snapshots, while for all other systems, snapshots were extracted from the whole 10 ns trajectories. For all extracted snapshots, the peptides were re-centered in their water boxes before the quantum-chemical calculations.