# Multi generated topology

**URL:** <https://gromacs.bioexcel.eu/t/multi-generated-topology/4278>\
**Category:** User discussions\
**Created:** [June 7, 2022, 7:46pm UTC](https://gromacs.bioexcel.eu/t/multi-generated-topology/4278 "2022-06-07T19:46:40Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![mw00847](https://avatars.discourse-cdn.com/v4/letter/m/ecd19e/32.png) [@mw00847](https://gromacs.bioexcel.eu/u/mw00847)\
**Post date:** [June 7, 2022, 7:46pm UTC](https://gromacs.bioexcel.eu/t/multi-generated-topology/4278/1 "2022-06-07T19:46:40Z")

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GROMACS version: 2021  
GROMACS modification: Yes/No

How can I/should I use more than one molecule with automated topology in a simulation.

Current top file reads,

#include “oplsaa.ff/forcefield.itp”

; included polypargen molecules

#include “atoms.itp”

#include “PEA.itp”  
#include “XYL.itp”  
#include “MES.itp”  
#include “TMB.itp”

Here the atom types are grouped together in atoms.itp, does this cause the correct atom types to be read as grompp will produce an error.

Any advice is greatly appreciated

James

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<div class="post-metadata">

**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:** [June 8, 2022, 2:13am UTC](https://gromacs.bioexcel.eu/t/multi-generated-topology/4278/2 "2022-06-08T02:13:57Z")

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As long as all new atom types or any other parameters are declared before any `[moleculetype]` is introduced, it’s fine.