[gmx-users] Improper dihedral parameters for peptide bond

[Dawid das]

Dear All,

I would like to make sure whether these parameters


O       X       X       C       2       0.0000  1004.16
NH1     X       X       H       2       0.0000  167.36

under [ dihedraltypes ] card in ffbonded.itp file are the improper dihedral
parameters for the peptide bonds as defined in aminoacids.rtp file with
the following statement:

 [ impropers ]
        N       -C      CA      HN
        C       CA      +N      O

If so, why isn't it C X X O if the first atom should be the to which all
the
others are connected?

Best Regards,
Dawid

PS I have sent the same question to a different address. I apologize  if I
doubled the topic.