For the calculation of the local-mode frequencies and coupling constants using vibrational maps, we applied the AIM program , using the maps and parameters as described above. To allow for the treatment of the ACE and NME caps in AIM, we used a locally modified version . For the 1GPB helix and for Trpzip2, the chloride ion was deleted from the corresponding PDB file before the AIM calculation. Input scripts for AIM are included in the supplementary data set .