# Atomtype CJ not found **URL:** \ **Category:** User discussions\ **Created:** [April 25, 2023, 10:46am UTC](https://gromacs.bioexcel.eu/t/atomtype-cj-not-found/6274 "2023-04-25T10:46:50Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Abhi\_Sahu](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/abhi_sahu/32/2111_2.png) [@Abhi\_Sahu](https://gromacs.bioexcel.eu/u/Abhi_Sahu)\ **Post date:** [April 25, 2023, 10:46am UTC](https://gromacs.bioexcel.eu/t/atomtype-cj-not-found/6274/1 "2023-04-25T10:46:50Z")
GROMACS version: 2020 GROMACS modification: No Command line: gmx grompp -f ions.mdp -c solv.gro -p gra.top -o ions.tpr Ignoring obsolete mdp entry ‘title’ Ignoring obsolete mdp entry ‘ns\_type’ NOTE 1 [file ions.mdp]: With Verlet lists the optimal nstlist is \>= 10, with GPUs \>= 20. Note that with the Verlet scheme, nstlist has no effect on the accuracy of your simulation. Setting the LD random seed to 646744793 Generated 461266 of the 461280 non-bonded parameter combinations Generating 1-4 interactions: fudge = 0.5 Generated 461280 of the 461280 1-4 parameter combinations ERROR 1 [file gra.top, line 34]: **Atomtype CJ not found** There was 1 note * * * Program: gmx grompp, version 2020.1-Ubuntu-2020.1-1 Source file: src/gromacs/gmxpreprocess/toppush.cpp (line 1408) Fatal error: There was 1 error in input file(s) For more information and tips for troubleshooting, please check the GROMACS website at [Common Errors — GROMACS webpage https://www.gromacs.org documentation](http://www.gromacs.org/Documentation/Errors) What to do? PS: Atom type is CJ in my Graphene topology file ---
**Author:** ![jalemkul](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/jalemkul/32/18_2.png) [@jalemkul](https://gromacs.bioexcel.eu/u/jalemkul)\ **Post date:** [April 25, 2023, 12:41pm UTC](https://gromacs.bioexcel.eu/t/atomtype-cj-not-found/6274/2 "2023-04-25T12:41:57Z")
CJ is not an atom type that is supported by any of the force fields that are natively in GROMACS. `grompp` is telling you that it can’t find it and therefore cannot assign LJ (or any other) parameters to it. ---
**Author:** ![Abhi\_Sahu](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/abhi_sahu/32/2111_2.png) [@Abhi\_Sahu](https://gromacs.bioexcel.eu/u/Abhi_Sahu)\ **Post date:** [April 26, 2023, 6:48am UTC](https://gromacs.bioexcel.eu/t/atomtype-cj-not-found/6274/3 "2023-04-26T06:48:09Z")
What can I do about it? Do I need to edit the force field files? ---
**Author:** ![jalemkul](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/jalemkul/32/18_2.png) [@jalemkul](https://gromacs.bioexcel.eu/u/jalemkul)\ **Post date:** [April 27, 2023, 4:54pm UTC](https://gromacs.bioexcel.eu/t/atomtype-cj-not-found/6274/4 "2023-04-27T16:54:54Z")
How did you generate the topology? What tool or program wrote a CJ atom type? ---
**Author:** ![Abhi\_Sahu](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/abhi_sahu/32/2111_2.png) [@Abhi\_Sahu](https://gromacs.bioexcel.eu/u/Abhi_Sahu)\ **Post date:** [April 29, 2023, 7:14am UTC](https://gromacs.bioexcel.eu/t/atomtype-cj-not-found/6274/5 "2023-04-29T07:14:57Z")
Thank you for responding I am following Andrea’s website for generating Carbon Nanotube topology please take a look at it [Modeling Carbon Nanotubes with GROMACS - Chembytes](http://chembytes.wikidot.com/grocnt) ---
**Author:** ![jalemkul](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/jalemkul/32/18_2.png) [@jalemkul](https://gromacs.bioexcel.eu/u/jalemkul)\ **Post date:** [April 29, 2023, 10:46am UTC](https://gromacs.bioexcel.eu/t/atomtype-cj-not-found/6274/6 "2023-04-29T10:46:18Z")
The first steps of the tutorial walk you through creating a custom force field for this system. Follow those steps to build the system.