# Gromacs file and analysis modification **URL:** \ **Category:** User discussions\ **Created:** [November 25, 2025, 5:42am UTC](https://gromacs.bioexcel.eu/t/gromacs-file-and-analysis-modification/12973 "2025-11-25T05:42:34Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![saad1877](https://avatars.discourse-cdn.com/v4/letter/s/ac8455/32.png) [@saad1877](https://gromacs.bioexcel.eu/u/saad1877)\ **Post date:** [November 25, 2025, 5:42am UTC](https://gromacs.bioexcel.eu/t/gromacs-file-and-analysis-modification/12973/1 "2025-11-25T05:42:34Z")
GROMACS version: 2025 GROMACS modification: Yes Here, post your question: I have run protein-ligand MD simulation for 500ns, but it ended before completion because of the power supply disruption. Now I want to perform analysis for only 200ns (md run was stopped at ~340ns). Please guide me if I can do such type of modification, if yes, then how? ---
**Author:** ![Karis](https://avatars.discourse-cdn.com/v4/letter/k/ed8c4c/32.png) [@Karis](https://gromacs.bioexcel.eu/u/Karis)\ **Post date:** [November 25, 2025, 5:49am UTC](https://gromacs.bioexcel.eu/t/gromacs-file-and-analysis-modification/12973/2 "2025-11-25T05:49:10Z")
Most gromacs functions should have the option to specify the times in the simulation which the function is being applied to, usually -b and -e to specify the beginning and end frames (for example, see the documentation for [gmx trjconv](https://manual.gromacs.org/documentation/current/onlinehelp/gmx-trjconv.html)), if you check the documentation for whichever function you’re trying to use, there should be similar instructions ---
**Author:** ![saad1877](https://avatars.discourse-cdn.com/v4/letter/s/ac8455/32.png) [@saad1877](https://gromacs.bioexcel.eu/u/saad1877)\ **Post date:** [November 25, 2025, 9:55am UTC](https://gromacs.bioexcel.eu/t/gromacs-file-and-analysis-modification/12973/3 "2025-11-25T09:55:18Z")
Thank you so much, I will try it.