# Constant force steered molecular dynamics (CF-SMD)

**URL:** <https://gromacs.bioexcel.eu/t/constant-force-steered-molecular-dynamics-cf-smd/2909>\
**Category:** User discussions\
**Tags:** mdrun\
**Created:** [October 5, 2021, 5:30am UTC](https://gromacs.bioexcel.eu/t/constant-force-steered-molecular-dynamics-cf-smd/2909 "2021-10-05T05:30:09Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![KailashB](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/kailashb/32/1041_2.png) [@KailashB](https://gromacs.bioexcel.eu/u/KailashB)\
**Post date:** [October 5, 2021, 5:30am UTC](https://gromacs.bioexcel.eu/t/constant-force-steered-molecular-dynamics-cf-smd/2909/1 "2021-10-05T05:30:09Z")

</div>

GROMACS version: 2018.1  
GROMACS modification: No  
Here post your question : how to perform steered molecular dynamics with application of constant force (CF-SMD)?  
From the mdp options of COM pulling from gromacs manual, I tried to perform CF-SMD (mdp options and result of this simulations is attached below), I got constant force graph but molecule did not extend (extension=0).  
; Pull code  
pull = yes  
pull\_ncoords = 1 ; only one reaction coordinate  
pull\_ngroups = 2 ; two groups defining one reaction coordinate  
pull\_group1\_name = Chain\_A  
pull\_group2\_name = Chain\_B  
pull\_coord1\_type = constant-force ; harmonic potential  
pull\_coord1\_geometry = distance ; simple distance increase  
pull\_coord1\_dim = Y N N  
pull\_coord1\_groups = 1 2  
pull\_coord1\_start = yes ; define initial COM distance \> 0  
pull\_coord1\_k = 500 ; kJ mol^-1 nm^-2

Can anyone suggest me if I am missing something or this is not the way for performing constant force SMD and if so how I can perform CF-SMD.

![extension-t](https://europe1.discourse-cdn.com/flex017/uploads/bioexcel1/original/2X/c/cb5dbb97ec4da754c9125631b51ccc6619c41af1.png)