# How to model air in gromacs?

**URL:** <https://gromacs.bioexcel.eu/t/how-to-model-air-in-gromacs/8022>\
**Category:** User discussions\
**Tags:** simulation-setup\
**Created:** [January 10, 2024, 7:19am UTC](https://gromacs.bioexcel.eu/t/how-to-model-air-in-gromacs/8022 "2024-01-10T07:19:21Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![keinerfan](https://avatars.discourse-cdn.com/v4/letter/k/e495f1/32.png) [@keinerfan](https://gromacs.bioexcel.eu/u/keinerfan)\
**Post date:** [January 10, 2024, 7:19am UTC](https://gromacs.bioexcel.eu/t/how-to-model-air-in-gromacs/8022/1 "2024-01-10T07:19:21Z")

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GROMACS version:  
GROMACS modification: Yes/No  
Here post your question  
hello  
i want to perform md simulation of silica nanoparticles at the water/air interface i built the system with packmol( 300 water molecules were added to my system to represent air) and proceed to em and encountered this error:  
Fatal error:  
There are inconsistent shifts over periodic boundaries in a molecule type  
consisting of 447 atoms. The longest distance involved in such interactions is  
5.813 nm which is above half the box length. Either you have excessively large  
distances between atoms in bonded interactions or your system is exploding.

can anyone help me with this? is there any better way to model air?

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**Author:** ![milosz.wieczor](https://avatars.discourse-cdn.com/v4/letter/m/b19c9b/32.png) [@milosz.wieczor](https://gromacs.bioexcel.eu/u/milosz.wieczor)\
**Post date:** [January 10, 2024, 11:20am UTC](https://gromacs.bioexcel.eu/t/how-to-model-air-in-gromacs/8022/2 "2024-01-10T11:20:01Z")

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It doesn’t really look like a problem with air/water, but perhaps with your nanoparticle (or another component that has 447 atoms). It might be broken through periodic boundary conditions, or another unexpected thing is happening.