Reg: Temperature rise in multi walled CNT + water system after equilibrium

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#1

Dear All,

I am simulating a system of 3 walled CNT + water molecules in lammps. AIREBO for CNT and TIP3P model for water. The system is equilibrated using fix NVE and fix NPT commands. After equilibration, the temperature of MWCNT is raised keeping the temperature of water same as that of equilibration. This is followed by allowing the energy to transfer from CNT to water in NVE ensemble.

After some time steps, when the temperature of CNT is reduced to the temperature of water molecules, it is assumed that the system has reached equilibrium.

The problem which I am facing in the simulation is that after the system reaches equilibrium, the temperature of the system again increases. It means that the temperature of 3 walled CNT and water again rises as the simulation is continued further after reaching equilibrium.
According to me, once the system reaches equilibrium, it should continue to remain in equilibrium even after continuing the simulation. But this is not the case for me.
PS. This problem has not been seen during the simulation of 2 walled CNT + water.

Thanks for the help.

#2

your description is quite vague and confusing and it is not clear what
you are asking. it seems that you have made some observations, but
there is no indication of whether this is a systematic issue or just
observation from a single run. with so little information about what
you did in terms of LAMMPS input settings and simulation times, it is
basically impossible to give any kind of specific advice. you don't
even say which version of LAMMPS you are using...

more importantly, have you confirmed, that your simulation protocol
and settings work for both, the CNT and the water independently (i.e.
a simulation of the CNT in vacuum and a pure bulk water system).

in general, there are *lots* of ways to make mistakes when doing
complex simulations.

axel.