# Change of box shape **URL:** \ **Category:** User discussions\ **Created:** [August 15, 2020, 3:48pm UTC](https://gromacs.bioexcel.eu/t/change-of-box-shape/670 "2020-08-15T15:48:15Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![mayank](https://avatars.discourse-cdn.com/v4/letter/m/bc8723/32.png) [@mayank](https://gromacs.bioexcel.eu/u/mayank)\ **Post date:** [August 15, 2020, 3:48pm UTC](https://gromacs.bioexcel.eu/t/change-of-box-shape/670/1 "2020-08-15T15:48:15Z")
GROMACS version: 2020.1 GROMACS modification: No I prepared a system taking toluene as a solvent and cubic box with a box size of 1.0. till the NVT step box was cubic but after NPT step box shape changes from cubic to rectangular. both NPT and NVT was run for 5ns. I am attaching the image of the box. How can I fix it? ![WhatsApp Image 2020-08-12 at 10.33.52 AM](https://europe1.discourse-cdn.com/flex017/uploads/bioexcel1/original/1X/1af9be1add28fa1712037a15ba61bf5cde2c14be.jpeg) ---
**Author:** ![Dr\_DBW](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/dr_dbw/32/42_2.png) [@Dr\_DBW](https://gromacs.bioexcel.eu/u/Dr_DBW)\ **Post date:** [August 15, 2020, 11:57pm UTC](https://gromacs.bioexcel.eu/t/change-of-box-shape/670/2 "2020-08-15T23:57:36Z")
Use isotropic pressure coupling instead of anisotropic/semisotropic. As you’ve found out anisotropic and even semisotropic pressure coupling can get into a situation where the box will deform into a long rectangular box and will eventually crash due to the shorter dimensions being shorter than the cut-off distances. And this can even happen with just solvent boxes. ---
**Author:** ![mayank](https://avatars.discourse-cdn.com/v4/letter/m/bc8723/32.png) [@mayank](https://gromacs.bioexcel.eu/u/mayank)\ **Post date:** [August 16, 2020, 6:46am UTC](https://gromacs.bioexcel.eu/t/change-of-box-shape/670/3 "2020-08-16T06:46:36Z")
Thank you for the advice its working