how to use fene potential for bonds?

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1

Dear lammps users

I want to use fene potetial bond for simulation of polymer with lammps.

but during simulation, system is warninig: fene bond too long and finally breaks run.

how to use fene potential for bonds?

thanks

mousavi

2

Hello Mousavi,

There are two stages to that problem:

  1. Getting the warning, which tells you something is going unusually weird. You should know that a FENE bond has an asymptotic right limit (normally R0). When you get too close to the limit (where “too” can be quantified by looking at the LAMMPS source code) LAMMPS flags the warning.

  2. The bond becomes longer than the R0 -> the simulation breaks.

You have to ask yourself why the bonds are stretching in such a weird manner since that is not supposed to happen. Most likely that is the result of a bad structure.

Best,

Nicola

3

You should give more information (such as a lammps input script and/or
starting configuration).

If you suspect a bad configuration, try generating a new configuration or
reducing the time step. You may be able to increase the time step again
once you have gotten away from the bad configuration. Also try running the
system for some time before adding temperature/coupling if using those. You
can also attempt to slowly adding pressure by adjusting Pstart and Pstop if
you are using that fix. You can also try adjusting the FENE parameters (R0
and K) and run for a short time to attempt to get past the bad config, and
then change them back to what you require for your production simulation.