[lammps-users] Partial freezing of the simulation box


I'm trying to simulate styrene-butadiene rubber using COMPASS forcefield in
lammps. NPT dynamics @353K and 1 atm runs normal for a certain amount of time
(~0.67 ns for the attached system) and then suddenly, most of the atoms in the
simulation box nearly freeze .
Any idea/suggestions to explain this?
Thank you,


in.SBR (848 Bytes)

restart.SBR_353K_0.5GPa.50000 (193 KB)

There's not enough information in your post. Have you
visualized the system? Is the energy going into some
other mode besides temperature? What does the system
thermodynamics do before this happens?


I have visualized the system(I tried attaching dcd file but it was rejected
since it's 6.3 MB). After running normally for a while, suddenly atoms move
around very quickly (faster than their normal motion) and during this time,
potential energy jumps (the log file attached) This lasts only for a few
femtoseconds. After this, only a few atoms keep
moving and potential energy drops.
Thanks for your help,


Quoting Steve Plimpton <[email protected]>:

SBR_353K_1atm.log (99 KB)

Dear Sezen,
As far as I can understand during the run, it seems like few atoms are getting very close to each other and (in the high vdwl repulsive zone) where they are not supposed to. (may be because of electrostatics or other interactions). This is happened with me also previously (1-4 atoms can come very close to each other at some dihedral values as there is not vdwl interactions between them, they can bring 1-5 atoms close enough to have a very high repulsive force and hence the start of what you are observing)