# If I increase the dt of mdp file , how does it affect to the final results?

**URL:** <https://gromacs.bioexcel.eu/t/if-i-increase-the-dt-of-mdp-file-how-does-it-affect-to-the-final-results/3479>\
**Category:** User discussions\
**Tags:** mdp-parameters, mdrun, simulation-setup\
**Created:** [January 14, 2022, 11:09am UTC](https://gromacs.bioexcel.eu/t/if-i-increase-the-dt-of-mdp-file-how-does-it-affect-to-the-final-results/3479 "2022-01-14T11:09:12Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Kalindu](https://avatars.discourse-cdn.com/v4/letter/k/eada6e/32.png) [@Kalindu](https://gromacs.bioexcel.eu/u/Kalindu)\
**Post date:** [January 14, 2022, 11:09am UTC](https://gromacs.bioexcel.eu/t/if-i-increase-the-dt-of-mdp-file-how-does-it-affect-to-the-final-results/3479/1 "2022-01-14T11:09:12Z")

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I have a system containing around 70 000 atoms. It is found that it takes a lot of time to complete the MD production run with dt = 0.002 (2 fs) in mdp file. If I change dt value, will it affect the simulation results badly?

GROMACS version:  
GROMACS modification: Yes/No  
Here post your question

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**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:** [January 14, 2022, 12:32pm UTC](https://gromacs.bioexcel.eu/t/if-i-increase-the-dt-of-mdp-file-how-does-it-affect-to-the-final-results/3479/2 "2022-01-14T12:32:55Z")

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You can’t arbitrarily increase the time step. The simulation will become unstable. There are approaches that involve virtual sites or redistribution of H masses that can allow for an increase in time step but you need to look into those carefully and no just increase `dt`.

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**Author:** ![Kalindu](https://avatars.discourse-cdn.com/v4/letter/k/eada6e/32.png) [@Kalindu](https://gromacs.bioexcel.eu/u/Kalindu)\
**Post date:** [January 14, 2022, 1:48pm UTC](https://gromacs.bioexcel.eu/t/if-i-increase-the-dt-of-mdp-file-how-does-it-affect-to-the-final-results/3479/3 "2022-01-14T13:48:00Z")

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Thank you for your advice !