# Coulomb cutoff for ion **URL:** \ **Category:** User discussions\ **Created:** [April 11, 2022, 10:02pm UTC](https://gromacs.bioexcel.eu/t/coulomb-cutoff-for-ion/3996 "2022-04-11T22:02:24Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![pinoji1](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/pinoji1/32/1442_2.png) [@pinoji1](https://gromacs.bioexcel.eu/u/pinoji1)\ **Post date:** [April 11, 2022, 10:02pm UTC](https://gromacs.bioexcel.eu/t/coulomb-cutoff-for-ion/3996/1 "2022-04-11T22:02:24Z")
GROMACS version:2020.1 GROMACS modification: No I have a rudimentary question regarding the calculation of solvation energies of charged species. Most examples so far seem to use a Coulomb cutoff of 1 nm or 1.2 nm for neutral species. For charged species, does the Coulomb cutoff need to be longer? Also, should the box size be increased accordingly? Or do I not need to worry about it since most interactions are cancelled during the DG calculation? Thank you very much. ---
**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:** [April 13, 2022, 2:33am UTC](https://gromacs.bioexcel.eu/t/coulomb-cutoff-for-ion/3996/2 "2022-04-13T02:33:51Z")
The cutoff is dictated by the force field and its conventions, not the chemical nature of the species. With PME, the electrostatic cutoff doesn’t matter a whole lot but you should remain consistent with the underlying force field, otherwise you risk breaking its assumptions and balance between LJ and electrostatic contributions. ---
**Author:** ![pinoji1](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/pinoji1/32/1442_2.png) [@pinoji1](https://gromacs.bioexcel.eu/u/pinoji1)\ **Post date:** [April 13, 2022, 1:45pm UTC](https://gromacs.bioexcel.eu/t/coulomb-cutoff-for-ion/3996/3 "2022-04-13T13:45:09Z")
Thank you very much for clarification!!