[gmx-users] impropers and residue number

[Lara Bunte]

Hello

I got this error:

Fatal error:
Atom ON1 is used in an interaction of type improper in the topology
database, but an atom of that name was not found in residue
number 1.


What do this mean? How to fix it? 


The Atom ON1 is declared in atomtypes.atp file. 


In my .rtp file I used [ impropers ] and I use a charmm27 force field.


Greetings