I am simulating CuO using the COMB potential. I created the crystal using the Crystallography Open Database and the Atomsk program. After replicating the cell 2 times in x and y just to run a simple check, I observed energy drain and temperature increase in the system. This is odd, and I’m sure I am doing something wrong. I also followed a conversation on the LAMMPS mailing list, which is about the same problem, but I couldn’t find a solution. I would appreciate your comment on the issue. Please find my code the following;
Please visualize your trajectory and review your thermo output.
Your system’s temperature “jumps” from the initial 300K to over 30,000K in 1000 MD steps. that is very, very bad and an indication that your initial geometry is not consistent with the potential. Also see the pressure and how quickly the volume changes (and thus the density).
the energy “drain” in this case is effectively the kinetic energy that the NPT thermostat is removing from your system to try and match your desired values.
but at step 20,000 your system is likely completely bogus.
to check energy conservation, you need a properly equilibrated structure and then run with fix nve, i.e. without a thermostat and a barostat.