# Problem with intermolecular restraints
**URL:** https://gromacs.bioexcel.eu/t/problem-with-intermolecular-restraints/235
**Category:** User discussions
**Created:** [June 3, 2020, 8:47am UTC](https://gromacs.bioexcel.eu/t/problem-with-intermolecular-restraints/235 "2020-06-03T08:47:20Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@amin\_sagar](https://gromacs.bioexcel.eu/u/amin_sagar)
#### Post date: [June 3, 2020, 8:47am UTC](https://gromacs.bioexcel.eu/t/problem-with-intermolecular-restraints/235/1 "2020-06-03T08:47:20Z")
GROMACS version: 2020
GROMACS modification: No
Dear All,
I am trying to simulate a protein-protein complex using Martini force field. The complex dissociates in the absence of any restraints. So, I am trying to impose distance restraints on the interface residues.
I wrote the following .itp file
; distance restraints for adam-vdw
[intermolecular\_interactions]
[distance\_restraints]
; ai aj type index type’ low up1 up2 fac
248 1335 1 0 1 0.0 0.3 0.4 1.0
The atom numbers are global.
I then included this file in the topology file as follows
#include “martini\_3.0.b.3.2/martini\_v3.0.b.3.2-1.3.itp”
#include “Protein\_A.itp”
#include “Protein\_B.itp”
#include “A-B-dist.itp”
#include “martini\_3.0.b.3.2/martini\_v3.0\_ions.itp”
#include “martini\_3.0.b.3.2/martini\_v3.0\_solvents.itp”
[system]
; name
Insanely solvated protein.
[molecules]
; name number
Protein\_A 1
Protein\_B 1
WN 40086
TNA 447
TCL 435
When I use this way to set up the simulation, I get the following error
Fatal error:
Syntax error - File A-B-dist.itp, line 2
Last line read:
‘[intermolecular\_interactions]’
Invalid order for directive intermolecular\_interactions
Could someone please help me in understanding the proper order or what else I am doing wrong here?
I would be grateful for any suggestions.
Best,
Amin.
---
### Author:  [@jalemkul](https://gromacs.bioexcel.eu/u/jalemkul)
#### Post date: [June 5, 2020, 12:14pm UTC](https://gromacs.bioexcel.eu/t/problem-with-intermolecular-restraints/235/2 "2020-06-05T12:14:45Z")
Intermolecular interactions have to be defined at the very end of the system `.top` file, as global atom numbers are only established after processing the `[molecules]` directive.
---
### Author:  [@amin\_sagar](https://gromacs.bioexcel.eu/u/amin_sagar)
#### Post date: [June 5, 2020, 12:51pm UTC](https://gromacs.bioexcel.eu/t/problem-with-intermolecular-restraints/235/3 "2020-06-05T12:51:10Z")
Thanks a lot. Works Perfectly.
Amin.