Biphasic system

I am building a biphasic system consisting of ethylbenzene and water. Using the gmx insert-molecule i created a box of dimension 15 15 4, with 2754 ethylbenzene molecule the maximum that could fit the box. Then did energy minimization and NVT equilibration. During the NVT equilibration i am facing the issue, the entire structure gets deformed as shown in the attached figure.

Any help would be appreciated
Thanking you

Constant volume simulation means the box size can’t change. That is not a deformation, it is the liquid getting to it’s correct simulation density. Obviously the density of the liquid is higher than what you generated so some areas form a “vacuum”. Best solution is to run NPT for awhile, get the density stable then return to your NVT settings.