# Error in computing the lateral diffusion in gromacs from tutorial2

**URL:** <https://gromacs.bioexcel.eu/t/error-in-computing-the-lateral-diffusion-in-gromacs-from-tutorial2/12593>\
**Category:** User discussions\
**Created:** [September 1, 2025, 5:06am UTC](https://gromacs.bioexcel.eu/t/error-in-computing-the-lateral-diffusion-in-gromacs-from-tutorial2/12593 "2025-09-01T05:06:34Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![raj\_kothari](https://avatars.discourse-cdn.com/v4/letter/r/919ad9/32.png) [@raj\_kothari](https://gromacs.bioexcel.eu/u/raj_kothari)\
**Post date:** [September 1, 2025, 5:06am UTC](https://gromacs.bioexcel.eu/t/error-in-computing-the-lateral-diffusion-in-gromacs-from-tutorial2/12593/1 "2025-09-01T05:06:35Z")

</div>

GROMACS version: 24  
GROMACS modification: Yes/No  
Here post your question : when I gave command gmx msd -s md\_0\_1.tpr -f md\_0\_1.xtc -n p8.ndx -lateral z from the tutorial and typed 20 (group P8), and did ^D, it did not get any value for lateral diffusion . It is showing as follows :

Specify any number of selections for option ‘sel’  
(Selections to compute MSDs for from the reference):  
(one per line, for status/groups, ‘help’ for help, Ctrl-D to end)

> 20  
> Selection ‘20’ parsed  
> Reading file md\_0\_1.tpr, VERSION 2024.2 (single precision)  
> Reading file md\_0\_1.tpr, VERSION 2024.2 (single precision)  
> Last frame 500 time 1000.000  
> Analyzed 501 frames, last time 1000.000
> 
> Please help; what should I do ?