# Omitting PBC

**URL:** <https://gromacs.bioexcel.eu/t/omitting-pbc/2132>\
**Category:** User discussions\
**Created:** [May 10, 2021, 2:29am UTC](https://gromacs.bioexcel.eu/t/omitting-pbc/2132 "2021-05-10T02:29:28Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![MOH4](https://avatars.discourse-cdn.com/v4/letter/m/a87d85/32.png) [@MOH4](https://gromacs.bioexcel.eu/u/MOH4)\
**Post date:** [May 10, 2021, 2:29am UTC](https://gromacs.bioexcel.eu/t/omitting-pbc/2132/1 "2021-05-10T02:29:28Z")

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Dear all,

Is there any way to omit PBC for simulation run?

I mean fisrtly I can use all steps and equilibrations and then for the final run (md.mdp) I can omit the PBC effect.

Thanks in advance.

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**Author:** ![alevilla](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/alevilla/32/439_2.png) [@alevilla](https://gromacs.bioexcel.eu/u/alevilla)\
**Post date:** [May 10, 2021, 9:05am UTC](https://gromacs.bioexcel.eu/t/omitting-pbc/2132/2 "2021-05-10T09:05:46Z")

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Hi,  
I am not sure I understand your question.  
But if the question was,can one run a simulation without periodic boundary condition? Yes, one can run without periodic boundary condition tuning the pbc option in mdp file.  
If the issue is how to deal with PBC effect, you can have a look to the following workflow  
[https://manual.gromacs.org/current/user-guide/terminology.html#suggested-workflow](https://manual.gromacs.org/current/user-guide/terminology.html#suggested-workflow)  
Best regards  
Alessandra

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<div class="post-metadata">

**Author:** ![MOH4](https://avatars.discourse-cdn.com/v4/letter/m/a87d85/32.png) [@MOH4](https://gromacs.bioexcel.eu/u/MOH4)\
**Post date:** [May 10, 2021, 10:11am UTC](https://gromacs.bioexcel.eu/t/omitting-pbc/2132/3 "2021-05-10T10:11:44Z")

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Dear Alessandra,  
Thanks for your response.

Yes, I want to run a simulation without PBC. Could you please tell me which line(s) in mdp should be changed?

Best

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<div class="post-metadata">

**Author:** ![alevilla](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/alevilla/32/439_2.png) [@alevilla](https://gromacs.bioexcel.eu/u/alevilla)\
**Post date:** [May 10, 2021, 11:55am UTC](https://gromacs.bioexcel.eu/t/omitting-pbc/2132/4 "2021-05-10T11:55:24Z")

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Hi,  
in the current version (2021) the option is not active. I think it was still active in 2019 or older version, you have to check the release note ([Release notes — GROMACS 2021.2 documentation](https://manual.gromacs.org/current/release-notes/index.html))  
In alternative you can use a very large box. On this topic please have a look at previous posts on vacuum simulation in this forum.  
best regards  
Alessandra