# How can I influence the number of steps in Gromacs simulation?

**URL:** <https://gromacs.bioexcel.eu/t/how-can-i-influence-the-number-of-steps-in-gromacs-simulation/362>\
**Category:** User discussions\
**Created:** [June 23, 2020, 1:21am UTC](https://gromacs.bioexcel.eu/t/how-can-i-influence-the-number-of-steps-in-gromacs-simulation/362 "2020-06-23T01:21:54Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![AglowRaph](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/aglowraph/32/167_2.png) [@AglowRaph](https://gromacs.bioexcel.eu/u/AglowRaph)\
**Post date:** [June 23, 2020, 1:21am UTC](https://gromacs.bioexcel.eu/t/how-can-i-influence-the-number-of-steps-in-gromacs-simulation/362/1 "2020-06-23T01:21:55Z")

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GROMACS version: 2020.1-Ubuntu-2020.1-1  
GROMACS modification: No

In nvt.mdp file during protein-ligand complex MD Simulation, you have:

> title = Protein-ligand complex NVT equilibration  
> define = -DPOSRES ; position restrain the protein and ligand  
> ; Run parameters  
> integrator = md ; leap-frog integrator  
> nsteps = 50000 ; 2 \* 50000 = 100 ps  
> dt = 0.002 ; 2 fs  
> ; Output control

So, I guessed that 0.02 \* 5000 = 100 ps and therefore changed the above values to this below:

> title = Protein-ligand complex NVT equilibration  
> define = -DPOSRES ; position restrain the protein and ligand  
> ; Run parameters  
> integrator = md ; leap-frog integrator  
> nsteps = 5000 ; 20 \* 5000 = 100 ps  
> dt = 0.02 ; 20 fs  
> ; Output control

But on using the command,

> gmx mdrun -deffnm nvt

I still get 50000 as number of steps for 100 ps.

HOW CAN I INFLUENCE THE NUMBER OF STEPS?

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<div class="post-metadata">

**Author:** ![Mikel](https://avatars.discourse-cdn.com/v4/letter/m/e480ec/32.png) [@Mikel](https://gromacs.bioexcel.eu/u/Mikel)\
**Post date:** [June 23, 2020, 7:02am UTC](https://gromacs.bioexcel.eu/t/how-can-i-influence-the-number-of-steps-in-gromacs-simulation/362/2 "2020-06-23T07:02:21Z")

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Greetings!

The mdp file is used by [grompp](http://manual.gromacs.org/documentation/current/onlinehelp/gmx-grompp.html) to create the tpr file.

This command

> [@AglowRaph](#):
>
> gmx mdrun -deffnm nvt

Is telling mdrun to read files with the prefix nvt, and so it will try to read a file called nvt.tpr, which most likely you created in a previous run trial. That is why your updated mdp file does not influence mdrun.

Summing up, you need to first run grompp with your new nvt.mdp file (check the link) to create a nvt.tpr file, and then run your mdrun command.

Let me know how it goes