Relaxation in Reaxff force field

Hello all
I establish a model of carbon materials (tetragraphene) based on the literature, and try to use the Reaxff force field (ffield.reax.cho) to relax it to obtain a stable structure .
But when I use the NPT system to relax the model, the pressure and potential energy cannot be stable, and the volume of the box is continuously changing.
I want to know why relaxation cannot be achieve.
Here is my input scripts

Here is some of the output of the press and energy

Thanks in advance for any advice.

The force field parameter set you are using is trained for combustion reactions. You need to find parameters that are better suited for your system. ReaxFF parameter sets are not very transferable. While it may sometimes look like it, but ReaxFF is not quantum chemistry.