# ERROR 1 rvdw-switch must be \< rvdw INQUIRY?

**URL:** <https://gromacs.bioexcel.eu/t/error-1-rvdw-switch-must-be-rvdw-inquiry/13282>\
**Category:** User discussions\
**Tags:** mdp-parameters\
**Created:** [March 5, 2026, 4:07pm UTC](https://gromacs.bioexcel.eu/t/error-1-rvdw-switch-must-be-rvdw-inquiry/13282 "2026-03-05T16:07:54Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![mjsubach](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/mjsubach/32/387_2.png) [@mjsubach](https://gromacs.bioexcel.eu/u/mjsubach)\
**Post date:** [March 5, 2026, 4:07pm UTC](https://gromacs.bioexcel.eu/t/error-1-rvdw-switch-must-be-rvdw-inquiry/13282/1 "2026-03-05T16:07:54Z")

</div>

GROMACS version: 2025.3  
GROMACS modification: Yes/No  
Here post your question:

Hello I CHARMM\_GUI generated a gromacs step6.0\_minimization.mdp file for a large transmembrane-ligand complex, the below error/notes were generated subsequent to Gromacs execution:

NOTE 1 [file step6.0\_minimization.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.

NOTE 2 [file step6.0\_minimization.mdp]: You have set rlist larger than the interaction cut-off, but you also have verlet-buffer-tolerance \> 0. Will set rlist using verlet-buffer-tolerance.

ERROR 1 [file step6.0\_minimization.mdp]: With switched vdw forces or potentials, rvdw-switch must be \< rvdw

The CHARMM\_GUI generated minimization.mdp file used is exhibited below:

 ![image](https://europe1.discourse-cdn.com/flex017/uploads/bioexcel1/original/2X/1/1a5b373841590b981409ca75b22e08fbb67fecaa.png)

In this case what would be the recommended modification i.e. maybe the rvdw\_switch to 0.9?

Thanks if you know:)

---

<div class="post-metadata">

**Author:** ![obZehn](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/obzehn/32/2629_2.png) [@obZehn](https://gromacs.bioexcel.eu/u/obZehn)\
**Post date:** [March 5, 2026, 5:41pm UTC](https://gromacs.bioexcel.eu/t/error-1-rvdw-switch-must-be-rvdw-inquiry/13282/2 "2026-03-05T17:41:11Z")

</div>

Hi @mjsubach

Is this CHARMM36m force field? In that case both `rcoulomb` and `rvdw` should be 1.2 nm, as you can see also in the [manual](https://manual.gromacs.org/documentation/current/user-guide/force-fields.html#charmm). This is happening because you are telling GROMACS to apply a force-switch modifier in the interval `rvdw_switch` - `rvdw`, which in this case would be a zero-width interval and would probably leave you with a discontinuity of the forces at the boundary.

Was this the direct output of CHARMM website?

---

<div class="post-metadata">

**Author:** ![mjsubach](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/mjsubach/32/387_2.png) [@mjsubach](https://gromacs.bioexcel.eu/u/mjsubach)\
**Post date:** [March 5, 2026, 6:24pm UTC](https://gromacs.bioexcel.eu/t/error-1-rvdw-switch-must-be-rvdw-inquiry/13282/3 "2026-03-05T18:24:26Z")

</div>

> [@obZehn](#):
>
> CHARMM36m force field

Hello obZehn thank you for your kind update:) and Google AI Mode indicates Yes, CHARMM-GUI Membrane Builder utilizes the CHARMM36m force field. And yes this was the CHARMM direct output. Accordingly I will modify as suggested, thanks again:)

---

<div class="post-metadata">

**Author:** ![obZehn](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/obzehn/32/2629_2.png) [@obZehn](https://gromacs.bioexcel.eu/u/obZehn)\
**Post date:** [March 5, 2026, 6:28pm UTC](https://gromacs.bioexcel.eu/t/error-1-rvdw-switch-must-be-rvdw-inquiry/13282/4 "2026-03-05T18:28:59Z")

</div>

CHARMM-GUI actually doesn’t support only CHARMM36m but they have also other FFs implemented, which you can chose when you are building your box. I never had this problem of getting the wrong vdw switch length in output, usually this is correctly set to 1.2 by CHARMM-GUI, that’s why I am asking. So double check the force field, but if it’s indeed CHARMM36m then go ahead with the parameters and electrostatics as listed in GROMACS manual! :)

---

<div class="post-metadata">

**Author:** ![mjsubach](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/mjsubach/32/387_2.png) [@mjsubach](https://gromacs.bioexcel.eu/u/mjsubach)\
**Post date:** [March 5, 2026, 8:44pm UTC](https://gromacs.bioexcel.eu/t/error-1-rvdw-switch-must-be-rvdw-inquiry/13282/5 "2026-03-05T20:44:05Z")

</div>

Hello obZehn thank you for your kind update:) and yes I streamed through CHARMM-GUI similarly to confirm and it is set by default to CHARMM36m, accordingly I modified as firstly indicated and it was executed and running, thanks:)