# Empty space in simulation

**URL:** <https://gromacs.bioexcel.eu/t/empty-space-in-simulation/3847>\
**Category:** User discussions\
**Created:** [March 16, 2022, 4:11pm UTC](https://gromacs.bioexcel.eu/t/empty-space-in-simulation/3847 "2022-03-16T16:11:34Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![JakubH](https://avatars.discourse-cdn.com/v4/letter/j/df788c/32.png) [@JakubH](https://gromacs.bioexcel.eu/u/JakubH)\
**Post date:** [March 16, 2022, 4:11pm UTC](https://gromacs.bioexcel.eu/t/empty-space-in-simulation/3847/1 "2022-03-16T16:11:34Z")

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GROMACS version: 2018.4  
GROMACS modification: No  
I tried to build a double bilayer system with a lower inside water layer hydration. I used bilayer to build that system and I deleted water molecules on one side in my copy and I put copy on my bilayer and you can see a bit empty space. Is it ok or maybe I should try to put some water there? Leaving this empty space can have some influents on my results? After I run simulation my results can be appropriate. And Is it possible to solvate in a specific coordinate, for example I want to put water molecules between 4.7 and 5 z coordinates. Is it possible?

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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 16, 2022, 5:39pm UTC](https://gromacs.bioexcel.eu/t/empty-space-in-simulation/3847/2 "2022-03-16T17:39:11Z")

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The void space will rapidly close and leave a very dehydrated interface between the two bilayers. They will interact unnaturally, I would expect.

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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 18, 2022, 1:46am UTC](https://gromacs.bioexcel.eu/t/empty-space-in-simulation/3847/4 "2022-03-18T01:46:48Z")

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Simulate it and see, but your water:lipid ratio still looks quite low and there appears to be a lot of smaller spaces that will compress very quickly. What is the water:lipid ratio in the system?