# Does the .gro file matter?

**URL:** <https://gromacs.bioexcel.eu/t/does-the-gro-file-matter/5664>\
**Category:** User discussions\
**Tags:** mdrun\
**Created:** [January 27, 2023, 4:44pm UTC](https://gromacs.bioexcel.eu/t/does-the-gro-file-matter/5664 "2023-01-27T16:44:52Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![oSalad](https://avatars.discourse-cdn.com/v4/letter/o/898d66/32.png) [@oSalad](https://gromacs.bioexcel.eu/u/oSalad)\
**Post date:** [January 27, 2023, 4:44pm UTC](https://gromacs.bioexcel.eu/t/does-the-gro-file-matter/5664/1 "2023-01-27T16:44:52Z")

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GROMACS version: 2018  
GROMACS modification: No

Hello,  
After solvation, energy minimization, equilibration, and running the production MD I get a .gro file. After looking at the contents of the .gro file, it just seems to hold coordinates. Are these gro files all the same thing or are they different? Also, when I try vmd productionMD.xtc [SOMETHING].gro, the simulation looks the same no matter what gro file I use (i.e. npt.gro or md.gro)

Thanks!

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<div class="post-metadata">

**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 27, 2023, 5:29pm UTC](https://gromacs.bioexcel.eu/t/does-the-gro-file-matter/5664/2 "2023-01-27T17:29:10Z")

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The final snapshot of a simulation is written to a `.gro` file by default. It will be redundant with the last frame of the trajectory but is often useful for quick visualization. Since GROMACS trajectories include t=0 and t=t(final) in the trajectory, you will get the same apparent appearance when loading a trajectory as data for a coordinate file.