Can I use two NVT for different group in one simulation?

Dear Prof. Axel,

Recently, I am working on some water confinement MD simulations using LAMMPS. About my model, there are mainly two parts, i.e. the first one is water, and the other is an unfixed nanotube. I have two questions:

  1. If I impose NVT ensemble for the whole system (like the command below), although the temperature of the system is maintained at 300K very well, the temperature of water is slightly larger than the targeted 300K with a decreasing trend. And the energy (total, potential) is not a constant averagely, which have a slight decreasing trend (The slope is only about 5, the intercept is in the order of 10^7). I wonder if this system can be considered as equilibrium state. I discussed that the slightly decreasing trend of energy is caused by the calculation of electrostatic force (PPPM method) and it’s difficult to eliminate, is it right?

Fix 1 movepart nvt temp 300.0 300.0 100.0

  1. I tried to impose NVT separately (like the command s below), the temperature can be maintained very well. However, I am confused that can I use these two NVT meanwhile?

fix 1 NT nvt temp 300.0 300.0 100.0

fix 2 water nvt temp 300.0 300.0 100.0

Hope to hear from soon. Thank you very much.

Best Regards,