Dear All,
could anyone advice me how to achieve a real value of density for polymer system? What approximately parameters of equilibration do I need to use? In my problem, I have a model of polyethylene, but after energy and temperature equilibration, a density value equals ≈0,82-0,83 g/cm^3 (the real value =0,9-097 g/cm^3 , literature value for such system reached 0,87-0,95 g/cm^3).
Thank you in advance for any suggestions,
Iryna
If you please explain me the main stages of building the model, maybe I will understand what the error is. I built models with Packmol and Material Studio separately, but results was the same
Iryna Omelchuk it depends on a few factors. What ensemble are you using? It's possible that the pressure of your simulation cell is different from the experimental reference values you want to obtain. Once you correct your simulation cell size for the target pressure, you can check whether it solves the mismatch between your simulations and the reference.
Shaswat Mohanty, I use NPT ensemble with the set pressure 0.1 MPa, but even after 10 ns this parameter may have wide amplitude when temperature has fluctuation ≈10-12 K. I tried to start simulation from 0,5 g/cm^3 and 0,9 g^3, but everytime I get the same result. As I understand, the pressure also need to stabilizate? Maybe you can advice some literature about pressure in MD simulation?
Iryna Omelchuk I'm assuming that's consistent with the pressure (close to 1 atm) at which the experimental density is reported?
Just check how much your volume fluctuates during your NPT simulation. Once your system equilibrates you can fix the box at the average size of the volume fluctuations and see what your resulting density is.