# Gmx insert-molecules for adding 4 kinds of different molecules

**URL:** <https://gromacs.bioexcel.eu/t/gmx-insert-molecules-for-adding-4-kinds-of-different-molecules/1004>\
**Category:** User discussions\
**Created:** [October 25, 2020, 6:26pm UTC](https://gromacs.bioexcel.eu/t/gmx-insert-molecules-for-adding-4-kinds-of-different-molecules/1004 "2020-10-25T18:26:33Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![newbie](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/newbie/32/283_2.png) [@newbie](https://gromacs.bioexcel.eu/u/newbie)\
**Post date:** [October 25, 2020, 6:26pm UTC](https://gromacs.bioexcel.eu/t/gmx-insert-molecules-for-adding-4-kinds-of-different-molecules/1004/1 "2020-10-25T18:26:33Z")

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Hello,

I want to add four kinds of molecules to my simulation box. Should I use gmx insert-molecules in four steps? In each step, how can I add new molecules in the previous gro file?  
Is it possible to use gmx insert-molecules one time and add all the molecules simultaneously?

I will appreciate any help.

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**Author:** ![Dr\_DBW](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/dr_dbw/32/42_2.png) [@Dr\_DBW](https://gromacs.bioexcel.eu/u/Dr_DBW)\
**Post date:** [October 26, 2020, 3:19am UTC](https://gromacs.bioexcel.eu/t/gmx-insert-molecules-for-adding-4-kinds-of-different-molecules/1004/2 "2020-10-26T03:19:53Z")

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With each call of `gmx insert-molecules` you insert one type molecule, then use the output from that step as the input for the next to insert another type of molecule.

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<div class="post-metadata">

**Author:** ![newbie](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/newbie/32/283_2.png) [@newbie](https://gromacs.bioexcel.eu/u/newbie)\
**Post date:** [October 26, 2020, 8:07pm UTC](https://gromacs.bioexcel.eu/t/gmx-insert-molecules-for-adding-4-kinds-of-different-molecules/1004/3 "2020-10-26T20:07:20Z")

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@Dr_DBW  
Thank you so much.