# A box of water explodes in the y direction

**URL:** <https://gromacs.bioexcel.eu/t/a-box-of-water-explodes-in-the-y-direction/6163>\
**Category:** User discussions\
**Tags:** mdrun, analysis-tools, simulation-setup\
**Created:** [April 11, 2023, 10:14pm UTC](https://gromacs.bioexcel.eu/t/a-box-of-water-explodes-in-the-y-direction/6163 "2023-04-11T22:14:51Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![gluizcar](https://avatars.discourse-cdn.com/v4/letter/g/aeb1de/32.png) [@gluizcar](https://gromacs.bioexcel.eu/u/gluizcar)\
**Post date:** [April 11, 2023, 10:14pm UTC](https://gromacs.bioexcel.eu/t/a-box-of-water-explodes-in-the-y-direction/6163/1 "2023-04-11T22:14:51Z")

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GROMACS version: - 2020.1  
GROMACS modification: No

I’m running a simulation where I have a box with water in the dimensions:  
1.7 X 2.5 X 2.7  
with 377 molecules. I did the optimization with optmize.mdp and then I did the optimization with NPT.mdp putting the temperature at 300K. But the box explodes in the y direction. I tried lowering the pressure too but got the same result. Does anyone have any suggestions to resolve this error?

Some input details:  
NPT.mdp: dt = 0.002, nsteps = 50000  
rlist = rcoulomb = rvdw = 0.01  
tau\_p = 5.0  
compressibility = 0 4.5e-5 0 0 0 0  
ref\_p = 0 1 0 0 0 0  
periodic\_molecules = yes

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**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 11, 2023, 11:03pm UTC](https://gromacs.bioexcel.eu/t/a-box-of-water-explodes-in-the-y-direction/6163/2 "2023-04-11T23:03:11Z")

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> [@gluizcar](#):
>
> rlist = rcoulomb = rvdw = 0.01

These cutoffs are about 100x too short. You won’t get anything physically sensible with this nonbonded setup.