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.