# How to add phosphate ions in the gromacs

**URL:** <https://gromacs.bioexcel.eu/t/how-to-add-phosphate-ions-in-the-gromacs/852>\
**Category:** User discussions\
**Created:** [September 22, 2020, 10:43am UTC](https://gromacs.bioexcel.eu/t/how-to-add-phosphate-ions-in-the-gromacs/852 "2020-09-22T10:43:29Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![alexmathew](https://avatars.discourse-cdn.com/v4/letter/a/f4b2a3/32.png) [@alexmathew](https://gromacs.bioexcel.eu/u/alexmathew)\
**Post date:** [September 22, 2020, 10:43am UTC](https://gromacs.bioexcel.eu/t/how-to-add-phosphate-ions-in-the-gromacs/852/1 "2020-09-22T10:43:29Z")

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GROMACS version:  
GROMACS modification: Yes/No  
Here post your question  
How to add phosphate buffer instead of NaCl or KCL?  
I would like to run a simulation with Phosphate buffer to replicate exact experimental system,

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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:** [September 22, 2020, 6:27pm UTC](https://gromacs.bioexcel.eu/t/how-to-add-phosphate-ions-in-the-gromacs/852/2 "2020-09-22T18:27:30Z")

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Polyatomic species can be inserted with `gmx insert-molecules`, provided you have a coordinate file for whatever it is you need. Most experiments are conducted at such low concentration of such species that you will only get a few molecules in the simulation and their effects are irrelevant.