# Inserting small molecule in lipid bilayer

**URL:** <https://gromacs.bioexcel.eu/t/inserting-small-molecule-in-lipid-bilayer/1603>\
**Category:** User discussions\
**Created:** [February 16, 2021, 5:13pm UTC](https://gromacs.bioexcel.eu/t/inserting-small-molecule-in-lipid-bilayer/1603 "2021-02-16T17:13:57Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![kwaldner](https://avatars.discourse-cdn.com/v4/letter/k/ecc23a/32.png) [@kwaldner](https://gromacs.bioexcel.eu/u/kwaldner)\
**Post date:** [February 16, 2021, 5:13pm UTC](https://gromacs.bioexcel.eu/t/inserting-small-molecule-in-lipid-bilayer/1603/1 "2021-02-16T17:13:58Z")

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When inserting a small molecule at the center of lipid bilayer, say using gmx insert-molecule, is it common (and acceptable) to replace one (or maybe several) lipids in order to insert the small molecule? I tried using gmx insert-molecule without any replacement (without using the -replace flag) but the molecule would not insert and there is no output file as a result (my guess is there is too much steric clash). My lipid bilayer is ~128 lipids in total (64 per leaflet). My molecule is about 15 angstroms long.