# Isothermal compressibility

**URL:** <https://gromacs.bioexcel.eu/t/isothermal-compressibility/3825>\
**Category:** User discussions\
**Created:** [March 11, 2022, 9:03am UTC](https://gromacs.bioexcel.eu/t/isothermal-compressibility/3825 "2022-03-11T09:03:32Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![dr\_m\_ganj](https://avatars.discourse-cdn.com/v4/letter/d/9f8e36/32.png) [@dr\_m\_ganj](https://gromacs.bioexcel.eu/u/dr_m_ganj)\
**Post date:** [March 11, 2022, 9:03am UTC](https://gromacs.bioexcel.eu/t/isothermal-compressibility/3825/1 "2022-03-11T09:03:32Z")

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GROMACS version: 2018  
GROMACS modification: Yes/No  
Dear Prof. Lemkul,  
I’m simulating 4000 toluene in a box of simulation. Is it necessary to set the compressibility of toluene in the npt.mdp file or the compressibility of water is satisfying?  
Thank you

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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:** [March 11, 2022, 1:05pm UTC](https://gromacs.bioexcel.eu/t/isothermal-compressibility/3825/2 "2022-03-11T13:05:15Z")

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I have no idea how different the value is or if it might change the simulation results, but for a simple system like this, the value must be known so why wouldn’t you use the real compressibility?