# How to get RMSD from beginning to end after extending simulation

**URL:** <https://gromacs.bioexcel.eu/t/how-to-get-rmsd-from-beginning-to-end-after-extending-simulation/3778>\
**Category:** User discussions\
**Created:** [March 4, 2022, 6:03am UTC](https://gromacs.bioexcel.eu/t/how-to-get-rmsd-from-beginning-to-end-after-extending-simulation/3778 "2022-03-04T06:03:55Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Dipto43](https://avatars.discourse-cdn.com/v4/letter/d/a9a28c/32.png) [@Dipto43](https://gromacs.bioexcel.eu/u/Dipto43)\
**Post date:** [March 4, 2022, 6:03am UTC](https://gromacs.bioexcel.eu/t/how-to-get-rmsd-from-beginning-to-end-after-extending-simulation/3778/1 "2022-03-04T06:03:55Z")

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

Dear all,  
I performed 150ns simulation and the I extended to another 50 ns (total 200ns). I have faced problems in calculating RMSD from 1ns to 200 ns due to extending the simulation time  
My question is,  
How can I get RMSD from 1ns to 200 ns?

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**Author:** ![Minalde](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/minalde/32/1370_2.png) [@Minalde](https://gromacs.bioexcel.eu/u/Minalde)\
**Post date:** [March 5, 2022, 1:43am UTC](https://gromacs.bioexcel.eu/t/how-to-get-rmsd-from-beginning-to-end-after-extending-simulation/3778/2 "2022-03-05T01:43:16Z")

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Hello,

You can combine the xtc files from the 150 ns and 50 ns simulations using ‘gmx trjcat,’ and then calculate the rmsd for the combined trajectory.