Dear All

I'm running MD simulation on a system containing about 1000 atoms. I ran a simulation of 500ps+500ps, then I ran another one of 1000ps+1000ps, the results are slightly different. I read some other litteratures, systems about the some amount of atoms normally ran simulation less than 1000ps(equilibration+data collection). How can we decide simulation length? It's said "equilibration should be continue until the values of monitered properties including energy, temperature and pressure and also structural properties become stable". I used NVT ensemble, the temperature always fluactuates at 300+-10K for both run, and the energy is also very stable after the geometry optimization for both run.

The final status of the system for the first run is

Total enthalpy                  : -258648.617 kcal/mol

Total energy                    : -258615.727 kcal/mol

Temperature                     :  300.167 K

Pressure                        :   -0.005 GPa

Volume                          : 44062.074 A^3

Density                         :    1.438 g/cm^3

For the second ran is

Total enthalpy                  : -259527.427 kcal/mol

Total energy                    : -258667.744 kcal/mol

Temperature                     :  294.687 K

Pressure                        :   -0.136 GPa

Volume                          : 44062.074 A^3

Density                         :    1.438 g/cm^3

Then how can I decide simulation length?

Thank you.

Jingjing Bu