REAXFF

Dear LAMMPS users,

I constructed a system of polymer containing Thiophene and Fulerene by using Moltemplate with Gaff force field. The output files: “system.data”, “system.in”, “system.in.init”, “system.in.settings” are then used as input/data files for LAMMPS.

The annealing simulation was then performed by GAFF and the system is relaxed by using the REAXFF potential. The employed commands are:

pair_style reax/c NULL

pair_coeff * * ffield.reax.CHOS C H O S

But some problems are still present:

LAMMPS (23 Oct 2017)

OMP_NUM_THREADS environment is not set. Defaulting to 1 thread. (…/comm.cpp:90)

using 1 OpenMP thread(s) per MPI task

Reading data file …

orthogonal box = (43.1271 43.1271 43.1271) to (92.8729 92.8729 92.8729)

1 by 1 by 1 MPI processor grid

reading atoms …

806 atoms

reading velocities …

806 velocities

scanning bonds …

3 = max bonds/atom

scanning angles …

6 = max angles/atom

scanning dihedrals …

18 = max dihedrals/atom

scanning impropers …

2 = max impropers/atom

reading bonds …

1065 bonds

reading angles …

2100 angles

reading dihedrals …

3912 dihedrals

reading impropers …

176 impropers

Finding 1-2 1-3 1-4 neighbors …

special bond factors lj: 0 0 0.5

special bond factors coul: 0 0 0.833333

4 = max # of 1-2 neighbors

11 = max # of 1-3 neighbors

33 = max # of 1-4 neighbors

28 = max # of special neighbors

ERROR: Incorrect args for pair coefficients (…/pair_reaxc.cpp:288)

Last command: pair_coeff * * ffield.reax.CHOS C H O S

Could anyone help please?

With polymer/covalent force field such as GAFF, there must be multiple atom types for one element so your structure file might have contained more than 4 atom types. With ReaxFF, there is only 1 atom type per element. You need to make sure the number and sequence of atom types in the structure file match that in the pair_coeff command. Also, ReaxFF doesn’t use bonds, angles, dihedrals, impropers so you should delete them in the structure file.