[lammps-users] Change in energy (%) to say equilibrium reached

Hello LAMMPS users, I am using LAMMPS window version 19 March 2020. I have epoxy molecule and using reaxff mattsson force field. I equilibrated system using NPT ensemble at 300 K and 1 atm and tried to see effect of different timesteps. Here is plot Total Energy of system vs time (in ps). I see high drift initially for 200 ps later it decreases. I have query how much this drift must be allowed to say equilibrium reached in NPT ensemble. means (% change in energy)


it is not how much the energy drops that matters; you need to run at least until the potential(!) energy has plateaued, and that doesn’t seem to be the case in your graph.
but even a plateauing potential energy does not guarantee equilibrium. it is a prerequisite, but one cannot know whether this is just temporary and whether the system will eventually drop into another, lower energy state. It occasionally happens that your potential energy fluctuates around a flat value for a while and then drops a bit again. Yet in most cases that is a gamble that one has to take. it is impractical, if not impossible, to continue simulating until one can be certain.