[lammps-users] LAMMPS for polymers


I am new to LAMMPS and have been trying to simulate
linear polyethylene chains using united atom force
fields. I tried to use 'in.chain' and 'data.chain'
provided in '/lammps/tools' with some modifications to
start the simulation. But it keeps crashing on me and
my guess is its due to the magnitude of the resulting
forces. Those files in /tools are for FENE chains and
the units are reduced lj units. I dont have a good
feel for the reduced units and hence cant figure out a
way around them.

Can any one pls provide me with an example for the
input files for polymers with united atom potentals in
either regular or reduced units. Also, does any know a
method to generate the initial configuration of the

Thanx in advance


What modifications did you make to in.chain? My guess
is that those modifications are causing the crashes.
How far along in the run are the crashes occurring?
Perhaps the crashes are due to timesteps that are too

Unfortunately, I'm unable to provide you with example
input for a united atom polymer model, and as you
probably know, LAMMPS doesn't do the building of the
initial configurations for you. You might try writing
your own builder script in python using the pizza.py



If you changed the force field from FENE to
united-atom (and presumably the units from
lj to real), then you also need to change atom
distances in the polymer initial config, else
the system will blow up. So basically you
need someway to create a set of initial
chains that have the right monomer spacing.

You could probably coerce the tools/chain.f code
to do it with the correct choice of "sigma" ...