# Remove Coulomb interaction

**URL:** <https://gromacs.bioexcel.eu/t/remove-coulomb-interaction/11651>\
**Category:** User discussions\
**Tags:** simulation-setup\
**Created:** [February 28, 2025, 3:20pm UTC](https://gromacs.bioexcel.eu/t/remove-coulomb-interaction/11651 "2025-02-28T15:20:59Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![js\_gro](https://avatars.discourse-cdn.com/v4/letter/j/ac8455/32.png) [@js\_gro](https://gromacs.bioexcel.eu/u/js_gro)\
**Post date:** [February 28, 2025, 3:20pm UTC](https://gromacs.bioexcel.eu/t/remove-coulomb-interaction/11651/1 "2025-02-28T15:20:59Z")

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GROMACS version: 2018  
GROMACS modification: No  
I am trying to have this instuctions to prevent forming globules of polymer chain.  
NO coulomb interaction  
LJ cutoff set to 0.3 nm  
All-bonds constrained using SHAKE

Gromacs implementation:  
constraint\_algorithm = shake ; holonomic constraints  
constraints = all-bonds ;

; Nonbonded settings  
cutoff-scheme = Verlet ; Buffered neighbor searching  
ns\_type = grid ; search neighboring grid cells  
nstlist = 10 ; 20 fs, largely irrelevant with Verlet  
rlist = 0.3 ; Short-range cutoff for neighbor list  
rvdw = 0.3 ; Short-range van der Waals cutoff (in nm)

DispCorr = EnerPres ; account for cut-off vdW scheme

; Electrostatics  
coulombtype = Cutoff ; Turn off Coulomb interactions  
rcoulomb = 0.0 ; No electrostatic interactions

Getting error: With Verlet lists rcoulomb!=rvdw is not supported (except for  
rcoulomb\>rvdw with PME electrostatics)

What’s the best way to do it, without changing the topology file as i want to turn on the coulombic interaction later on.

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<div class="post-metadata">

**Author:** ![scheiber](https://avatars.discourse-cdn.com/v4/letter/s/e47774/32.png) [@scheiber](https://gromacs.bioexcel.eu/u/scheiber)\
**Post date:** [February 28, 2025, 6:26pm UTC](https://gromacs.bioexcel.eu/t/remove-coulomb-interaction/11651/2 "2025-02-28T18:26:39Z")

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The correct way to do this is to set the charges on all atoms to 0. If you want to make this reversible, then use a user-defined variable in your MDP file, for example

`define = -DZEROCHARGE`

Then in your topology file(s) you could use an [ifdef statement](https://manual.gromacs.org/documentation/2025.0/reference-manual/topologies/topology-file-formats.html#ifdef-statements)

```auto
#ifdef ZEROCHARGE
[atoms]
<define atoms with zero charge here>
#else
[atoms]
<define atoms with normal charge here>
#endif

```

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<div class="post-metadata">

**Author:** ![js\_gro](https://avatars.discourse-cdn.com/v4/letter/j/ac8455/32.png) [@js\_gro](https://gromacs.bioexcel.eu/u/js_gro)\
**Post date:** [March 4, 2025, 9:26pm UTC](https://gromacs.bioexcel.eu/t/remove-coulomb-interaction/11651/3 "2025-03-04T21:26:11Z")

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Do I also need to redefine the residue in the `.atp` file? I added the `#ifdef` statement in the OPLS-AA non-bonded section, but when running `gmx pdb2gmx` or performing minimization, the `define` function is not executing correctly.

Is there a way to implement the WCA potential in GROMACS, similar to how the “shift” command is used in LAMMPS?