# Inculding a replusion force between selected atoms for sMD **URL:** \ **Category:** User discussions\ **Tags:** mdp-parameters\ **Created:** [December 4, 2023, 7:22pm UTC](https://gromacs.bioexcel.eu/t/inculding-a-replusion-force-between-selected-atoms-for-smd/7788 "2023-12-04T19:22:04Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![krb0073](https://avatars.discourse-cdn.com/v4/letter/k/977dab/32.png) [@krb0073](https://gromacs.bioexcel.eu/u/krb0073)\ **Post date:** [December 4, 2023, 7:22pm UTC](https://gromacs.bioexcel.eu/t/inculding-a-replusion-force-between-selected-atoms-for-smd/7788/1 "2023-12-04T19:22:04Z")
GROMACS version:2022.2 GROMACS modification: No Here post your question Hello All, I am trying to create a configuration file for a steered MD simulation of the membrane protein KvAP. I am following the methods laid out by the paper _The Voltage-Dependent Deactivation of the KvAP Channel Involves the Breakage of Its S4 Helix_ (doi: [https://doi.org/10.3389/fmolb.2020.00162](https://doi.org/10.3389/fmolb.2020.00162)), but I am having difficulty find the parameters to quote " [have] the alpha carbon atoms repelled by each other by a force of 23 kJ/mol/nm" . As of writing this, I have not found the correct setting. Any input would be appreciated, -Kyle ---
**Author:** ![hess](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/hess/32/416_2.png) [@hess](https://gromacs.bioexcel.eu/u/hess)\ **Post date:** [December 5, 2023, 10:17am UTC](https://gromacs.bioexcel.eu/t/inculding-a-replusion-force-between-selected-atoms-for-smd/7788/2 "2023-12-05T10:17:28Z")
I am not aware of the option of a constant force functionality between atom pairs, apart from the pull code. You could use the pull code, but that gets inconvenient when the number of pairs is high. But I would think that using constant repulsive forces between atom pairs is not the optimal setup.