# Gen\_vel=no and continuation=false

**URL:** <https://gromacs.bioexcel.eu/t/gen-vel-no-and-continuation-false/9094>\
**Category:** User discussions\
**Tags:** mdp-parameters, simulation-setup\
**Created:** [May 7, 2024, 2:44pm UTC](https://gromacs.bioexcel.eu/t/gen-vel-no-and-continuation-false/9094 "2024-05-07T14:44:29Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Alessandro](https://avatars.discourse-cdn.com/v4/letter/a/ac91a4/32.png) [@Alessandro](https://gromacs.bioexcel.eu/u/Alessandro)\
**Post date:** [May 7, 2024, 2:44pm UTC](https://gromacs.bioexcel.eu/t/gen-vel-no-and-continuation-false/9094/1 "2024-05-07T14:44:29Z")

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GROMACS version: 2023.4  
GROMACS modification: No  
Hi!  
I’m performing a 10μs simulation divided into 50 simulations of 200ns each. I set ‘gen\_vel=no’ in the mdp file, but I didn’t include ‘continuation=yes’. The simulations are working, but I can’t understand how GROMACS generates velocities. Also i didn’t include the grompp -f .cpt flag.

gmx grompp -f md\_0mV.mdp -c md\_0mV-001.gro -r md\_0mV-001.gro -p …/system\_60\_mol.top -n …/index.ndx -o md\_0mV-002.tpr  
gmx mdrun -v -deffnm md\_0mV-002 -ntmpi 1 -nt 10 -nb gpu  
Thank you everybody!

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**Author:** ![hess](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/hess/32/416_2.png) [@hess](https://gromacs.bioexcel.eu/u/hess)\
**Post date:** [May 13, 2024, 9:53am UTC](https://gromacs.bioexcel.eu/t/gen-vel-no-and-continuation-false/9094/2 "2024-05-13T09:53:04Z")

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The continuation option does not affect velocity generation. It controls whether the initial coordinates and velocities are constrained and whether the state of thermo- and barostat, when present, are taking from the checkpoint file (which you do not pass).

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**Author:** ![Karis](https://avatars.discourse-cdn.com/v4/letter/k/ed8c4c/32.png) [@Karis](https://gromacs.bioexcel.eu/u/Karis)\
**Post date:** [June 27, 2025, 7:33am UTC](https://gromacs.bioexcel.eu/t/gen-vel-no-and-continuation-false/9094/3 "2025-06-27T07:33:47Z")

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I had a similar question and wanted to confirm, if the mdp file has set gen\_vel=no and the grompp command doesn’t include a checkpoint file, are initial velocities still assigned to match the temperature set by the thermostat? In that case, is gen\_vel meant for a more specific purpose other than just setting the initial velocities or is it automatically set to yes if no checkpoint file is provided?

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**Author:** ![hess](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/hess/32/416_2.png) [@hess](https://gromacs.bioexcel.eu/u/hess)\
**Post date:** [July 22, 2025, 12:38pm UTC](https://gromacs.bioexcel.eu/t/gen-vel-no-and-continuation-false/9094/4 "2025-07-22T12:38:46Z")

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Only gen\_vel generates new velocities. Several other file formats also support velocities, such as gro and trr. When the no velocities are provided and gen\_vel=no, the initial velocities will all be zero.