I am applying ehex thermostat for the above structure. The Structure is a freestanding type (free surface) where boundary phonons exists (surface) and boundary scattering occurs in Z directional phonons. However, I am not getting steady system temperature. Rather the temperature is increasing in exponential amount.
This kind of unusual behavior does not happen when I do everything same except for a Bulk Structure (no free surface).
I confirm that my heat flux value is not a problem. What other issue might cause these kind of behavior in freestanding structure?