[lammps-users] hybrid reaxff with pair potential: is this possible?

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1

I'm new to lammps, and I am trying to look at a system in which an organic molecule is above the surface of an ionic material. I would like to describe the atoms in the molecule using the reaxff potential, and the atoms in the surface using a combination of Lennard-Jones and Coulomb interactions.

I have tried to do this using a hybrid/overlay pair style. Here is a fragment from the input file:

pair_style hybrid/overlay reax 10.0 0 1 1.0e-6 lj/cut/coul/long 10.0 12.2500
pair_coeff * * reax ffield.reax 1 3 2 NULL NULL
pair_coeff * * lj/cut/coul/long 0.000 0.000
pair_coeff 2 2 lj/cut/coul/long 2.206E-01 3.340
pair_coeff 2 4 lj/cut/coul/long 1.147E-01 3.315
pair_coeff 2 5 lj/cut/coul/long 1.409E-01 3.850
pair_coeff 4 4 lj/cut/coul/long 5.962E-02 3.290
pair_coeff 5 5 lj/cut/coul/long 9.002E-02 4.360
pair_coeff 4 5 lj/cut/coul/long 7.326E-02 3.825

However, when I try to run lammps I get the

ERROR: Invalid REAX atom type

message. Is it possible to do what I want to do? The manual page for the reax potential ( http://lammps.sandia.gov/doc/pair_reax.html ), says reax can be used as part of a hybrid potential, with NULL values used a placeholders for atom types that will be described by other potentials. Could anyone tell me if this is actually possible in LAMMPS?

Cheers

Clive

2

clive,

this topic came up recently and the resolution was that neither reax nor reax/c
currently support hybrid or hybrid/overlay. the interface between the lowlevel
reax or reax/c code and LAMMPS does handle the input as expected, but the
lowlevel code is not (yet) ready to deal with this. hence you get the
error message
that you are seeing.

sorry,
    axel.

p.s.: in case the lowlevel code gets adapted to handle hybrid use, what you want
to use would be plain hybrid and not hybrid/overlay.

3

What the code should do is flag use of ReaxFF with hybrid
as a not-possible error. I'll post a patch for this. It's going to take
some to enable that to work due to the way the ReaxFF library
is setup.

Steve

4

Both the reax and reax/c pair styles now disallow
use with pair hybrid. 6Feb11 patch enforces this.

Steve