Reaxff with polymers

Hello,

I’m new to lammps and I’ve written the following input script:

REAX potential for a bead spring polymer system

units real

atom_style charge

read_data data.polyethylene_100chains_100monomers_density0.95

pair_style reax 6.0 1 1 1.0e-6

pair_coeff * * ffield.reax 1 2

compute reax all pair reax

neighbor 0.3 bin

neigh_modify every 10 delay 0 check no

fix 1 all nve

fix 2 all temp/berendsen 300.0 300.0 100.0

fix 3 all reax/bonds 100 bonds.tatb

thermo 10

timestep 0.2

dump 1 all atom 30 dump.reax.polyethylene_100chains_100monomers.lammpstrj

run 100

The .data file was constructed via a polymer modeler and has been equilibrated . My question is if the reaxff is going to construct the initial structure(polyethylene), without changing it (because the only pair style that I could use was charge which does not contain bonds) plus the cross-links.

Many thanks in advance.

Best regards,

Mike

Hi,

21.06.2013, 17:58, "Michael Papanikolaou" <[email protected]>:

Hello,

...

The .data file was constructed via a polymer modeler and has been equilibrated . My question is if the reaxff is going to construct the initial structure(polyethylene), without changing it (because the only pair style that I could use was charge which does not contain bonds) plus the cross-links.

If by constructing the initial structure you mean determining bonding between monomers (and links between chains), whether Reax will find bonds or not depends on what parametrization of Reax you use and how did you construct and equilibrate your initial geometry. If atomic positions you have are more or less consistent with what would Reax give for polyethilene, bonds will be ok. Anyway, you have to check it. You may use fix reax/c/bonds and fix reax/c/species to see what you get.

Regards,
Oleg.

The input to ReaxFF is just atom positions so ReaxFF always tries to find bonds. A simple test is to read your structure into Lammps, run a minimization using ReaxFF and then a few steps of low temperature MD, output the structure and do a bond by bond comparison to your input structure. This will tell you if there are problems with the ReaxFF parameter file you are using, the input file structure or any other options set.

Kevin