Dear everyone,

I'm little confusing to obtain T-V diagram of pure polymer. We are trying to obtain polymer solution T-V diagram after this work.

I performed the MD for one chain polystyrene with COMPASS, Nose thermostat where Q ratio=1, Berendsen Barostat where Decay constant=0.1ps, 550K and 0.0000Gpa

While we performing this dynamics simulation, the temperature and density fluctuated gradually (from 100K to 1800K and from 0.4g/cc to 0.9g/cc) after 100 ps.

I performed this again and again, However, I couldn't relax this cell using Nose and Berendsen. Its density no make sense because the polystyrene have a density about 1.05g/cc at 550K.

In this purpose, I chose another thermostat, Andersen. This work showed better result than Nose thermostat.

Here is my question.

What is the difference between Nose and Andersen? Does the Nose thermostat not fit well for relaxing 100 repeat unit polymer?