# Error in pbc box defining

**URL:** <https://gromacs.bioexcel.eu/t/error-in-pbc-box-defining/8973>\
**Category:** User discussions\
**Created:** [April 24, 2024, 1:01pm UTC](https://gromacs.bioexcel.eu/t/error-in-pbc-box-defining/8973 "2024-04-24T13:01:38Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Vignesh666D](https://avatars.discourse-cdn.com/v4/letter/v/b9bd4f/32.png) [@Vignesh666D](https://gromacs.bioexcel.eu/u/Vignesh666D)\
**Post date:** [April 24, 2024, 1:01pm UTC](https://gromacs.bioexcel.eu/t/error-in-pbc-box-defining/8973/1 "2024-04-24T13:01:38Z")

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GROMACS version:  
GROMACS modification: Yes/No  
Here post your question  
I am working on the CG Simulations with large  
systems. During PBC definition I used gmx edifconf -f -bt cubic  
-d 1.0 -o tried this and also increased the box size 60 60 60. Then  
during ionisation, it showed an error which I have attached with the  
mail. I tried to solve this error by increasing the box size 80 80 80  
also still the same error message. Since I removed some water  
molecules after solvation do you think error because of that? In my  
mdp file list value is about 1.0. Kindly please help me. I look  
forward to hearing from you.  
Error : The cut-off length is longer than half the shortest box vector or longer than the smallest box diagonal element. Increase the box size or decrease the rlist

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**Author:** ![MagnusL](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/magnusl/32/2380_2.png) [@MagnusL](https://gromacs.bioexcel.eu/u/MagnusL)\
**Post date:** [April 24, 2024, 1:10pm UTC](https://gromacs.bioexcel.eu/t/error-in-pbc-box-defining/8973/2 "2024-04-24T13:10:07Z")

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A box size of 60 60 60 should definitely be enough. Could you post the full command line you used when getting that error? Could you post the last line of the .gro file you are using? What are your rvdw and rcoul values in your .mdp file?

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**Author:** ![Vignesh666D](https://avatars.discourse-cdn.com/v4/letter/v/b9bd4f/32.png) [@Vignesh666D](https://gromacs.bioexcel.eu/u/Vignesh666D)\
**Post date:** [April 24, 2024, 4:47pm UTC](https://gromacs.bioexcel.eu/t/error-in-pbc-box-defining/8973/3 "2024-04-24T16:47:08Z")

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cmd used in grompp :  
gmx grompp -f -c -p -o .tpr and the last line of the gro file was 0.00 0.00 0.00 and rvdw 1.2 I think gro file last line was the error. I found the issue was solved. Thankyou