Helix unfolding despite position restraints

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GROMACS version: 2022
GROMACS modification: No

Hi,

I’m equilibarting a system with 12 copies of the same alpha-helical peptide, so I’m using backbone position restraints as I’ve always used for the equilibration steps. But despite of the restraints some of the peptides keep unfolding when I run the NVT equilibration. To my knowledge this behavior should be impossible. The weird part is that only some of the peptides unfold, while others continue stable.

My postion restraint files is as follows

[ position_restraints ]
;  i funct       fcx        fcy        fcz
   1    1       1000       1000       1000
   5    1       1000       1000       1000
  23    1       1000       1000       1000
  25    1       1000       1000       1000
  27    1       1000       1000       1000
  45    1       1000       1000       1000
  47    1       1000       1000       1000
  49    1       1000       1000       1000
  64    1       1000       1000       1000
  66    1       1000       1000       1000
  68    1       1000       1000       1000
  84    1       1000       1000       1000
  86    1       1000       1000       1000
  88    1       1000       1000       1000
 106    1       1000       1000       1000
 108    1       1000       1000       1000
 110    1       1000       1000       1000
 128    1       1000       1000       1000
 130    1       1000       1000       1000
 132    1       1000       1000       1000
 147    1       1000       1000       1000
 149    1       1000       1000       1000
 151    1       1000       1000       1000
 166    1       1000       1000       1000
 168    1       1000       1000       1000
 170    1       1000       1000       1000
 188    1       1000       1000       1000
 190    1       1000       1000       1000
 192    1       1000       1000       1000
 209    1       1000       1000       1000
 211    1       1000       1000       1000
 213    1       1000       1000       1000
 228    1       1000       1000       1000

All my files can be found in the following link: Google Drive

Thanks