Error when extending a box in z dimesnion

GROMACS version: 2018.2
GROMACS modification: No

Hello All.

I’m trying to do some interfacial studies. and am new to gromacs. I first equilibriate a box of (9x9x9) nm3 of water using an NPT simulation, following which i extend the box in the z direction to create a (9x9x27)nm3 box. with vacuum spaces above and below the bulk using editconf. However when i do this, i get some very high forces on atoms (order of 10^10), which causes my simulation to blow up. I’m trying to circumvent this by energy minimizing the configuration file of the new box. However I’m not very convinced that this is the right way to do it. It would be very helpful if someone could suggest a way to implement the box change without an energy minimization.