Dear friends, 

I am preparing polymer structure according to this procedure: (1) simulation cell prepared at low density, (2) compression of simulation box using NPT ensemble at higher pressure, (3) annealing using NPT ensemble and (4) MD runs with NPT and then NVT ensembles (iterative until it shows signs of equilibration. At the last step, I expect the density of the polymer structure will maintain (MD run with NVT ensemble) as compared to the density obtained in previous MD/NPT run. What does it mean when the density from MD/NVT run is different compared to its previous MD/NPT run? Appreciate your sharing. Thanks.