# Pdb2gmx fatal error: residue naming **URL:** \ **Category:** User discussions\ **Created:** [May 10, 2024, 1:18pm UTC](https://gromacs.bioexcel.eu/t/pdb2gmx-fatal-error-residue-naming/9124 "2024-05-10T13:18:53Z")\ **Posts on this page:** 1\ **Showing post:** 3
**Author:** ![ivangreg](https://avatars.discourse-cdn.com/v4/letter/i/7993a0/32.png) [@ivangreg](https://gromacs.bioexcel.eu/u/ivangreg)\ **Post date:** [May 13, 2024, 5:41pm UTC](https://gromacs.bioexcel.eu/t/pdb2gmx-fatal-error-residue-naming/9124/3 "2024-05-13T17:41:07Z")
Hi @scinikhil Would you mind pointing to a thread showing a solution to this problem? I ask because I have asked a similar question to the forum but in my case is about n-terminal acetylation (residue ACE): > [@Pdb2gmx: Fatal error: Atom CA in residue ACE 1 was not found in rtp entry ACE](https://gromacs.bioexcel.eu/t/pdb2gmx-fatal-error-atom-ca-in-residue-ace-1-was-not-found-in-rtp-entry-ace/9103): > > GROMACS version: 2024.1 GROMACS modification: No Hello community. I am trying to reproduce a tutorial for [umbrella sampling](http://www.mdtutorials.com/gmx/umbrella/index.html). In it, the [preparation of the topology](http://www.mdtutorials.com/gmx/umbrella/01_pdb2gmx.html) is shown as follows: gmx pdb2gmx -f 2BEG\_model1\_capped.pdb -ignh -ter -o complex.gro What I am trying to do is run that command selecting a CHARMM36 force-field: gmx pdb2gmx -f 2BEG\_model1\_capped.pdb -ff charmm36\_ljpme-jul2022 -ignh -ter -o complex.pdb However, that command throws this error: Fatal error: Atom CA in residue A… Yet, I haven’t got any pointers to a solution. In my experience, with this particuler error, the forum is very useful to understand what the problem is but there are no solutions reported. I find hard to believe that simple problems like this remain unresolved. As you say, it must have been discussed and solved many times. Thank you. Ivan --- _[View the full topic](https://gromacs.bioexcel.eu/t/pdb2gmx-fatal-error-residue-naming/9124)._