Regarding Stabilizing the plates

Greetings of the day…!

Dear All.

In my work, I am simulating a PDMS coating to study the effect of substrate surface roughness on its mechanical behaviour. In order to do so, I am simulating a capped system that includes PDMS molecules in the middle, thick metal atom layers at the bottom to represents a substrate (that will be made rough at later stages) and top metal atom layers to be used to employ the boundary conditions. I am using multiple ensemble for different layers in order to stabilize the system. In order to equilibrate the pressure, I am allowing the top layer atoms to move in Z direction while maintaining their planarity. Polymer atoms are interacting with metal atoms using LJ potential only. While PDMS atoms are charged particles and metal atoms are LJ particles that are kept fixed using self spring.

Various fixes that I am using to simulate the desired system includes:

fix 1 Polymer nvt 600.0 600.0 20.0

fix 2 TopSubstrate npt temp 600 600 10 z 0 0 500

fix 3 TopSubstrate spring/self 2000 xy

fix 4 BottomSubstrate spring/self 2000 xyz

Now, my question is that is this procedure correct. If it is, then I want to mention that I am not able to stabilize the top plate as it either start moving downwards or upwards.

Thank you.

Best Regards