I was trying to optimize the below carbon nanotube with the equilibrium.in script, but the pressure and E_pair energy became zero and infinite, respectively. After running for a thousand steps, the situation didn’t change. I observed the dumb file and found that all atom vanishes after a single step. I tried with a lower time step and a higher AIREBO cutoff, but found the same. Any suggestions regarding probable cause?
equilibrium.in (1014 Bytes)
CNT_6_0_0_x6.data (843.5 KB)
Hi @shoriful_Islam,
Please have a look at the guidelines post to help you investigate your problem and formulate your question at best. Note that this is a common issue so your likely to find a solution in the forum. If not you can ask a more detailed question explaining your problem.
Diverging pair energy and pressure are a common sign of bad geometry or wrong set of units. Also note that the input files your provide are wrong and leads to a format error when used because of the inconsistency between the atom types number and the Masses section of the data file.
Bad geometry. Most definitely. Once values are NaN or Inf, they won’t come back. So there is no point. The AIREBO cutoff parameter should remain at 3.0. Using a different value will result in incorrect spline tabulation. This is not flagged by LAMMPS as an error for backward compatibility.
The bad geometry can be easily confirmed by inserting something like:
delete_atoms overlap 0.1 all all
and checking the log file. In your case, there are a whopping 8160 atoms being deleted, i.e. being closer to each other by less than 0.1 angstrom. That is almost half of the atoms.