"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c

:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Section_commands.html#comm)

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pair_style reax command :h3

[Syntax:]

pair_style reax hbcut precision :pre

hbcut = hydrogen-bond cutoff (distance units)
precision = precision for charge equilibration :ul

[Examples:]

pair_style reax
pair_style reax 10.0 1.0e-5
pair_coeff * * ffield.reax C H O N :pre

[Description:]

The pair style computes the ReaxFF potential of van Duin, Goddard and
co-workers.  ReaxFF uses distance-dependent bond-order functions to
represent the contributions of chemical bonding to the potential
energy.  Details of the ReaxFF and its interatomic potential energy
calculation are given in the following publications: "(van Duin
2001)"_#van_Duin_2001 and "(van Duin 2003)"_#van_Duin_2003.

LAMMPS provides a ReaxFF potential file in its potentials dir, namely
potentials/ffield.reax.  Its format is identical to that used by van
Duin and co-workers.  It contains parameterizations for the following
elements: C, H, O, N, S, and Si.  You can use your another file in
place of it, and ReaxFF files with parameterizations for other
elements or for specific chemical systems may be available elsewhere.

The {hbcut} and {precision} settings are optional arguments.  If
neither is provided, default settings are used: {hbcut} = 10 (which is
Angstroms in real units) and {precision} = 1.0e-6 (one part in 10^6).
If you wish to override either of these defaults, then both settings
must be specified.

Use of this pair style requires that a charge be defined for every
atom since the potential performs charge equilibration.  See the
"atom_style"_atom_style.html and "read_data"_read_data.html commands
for details on how to specify charges.

The thermo variable {evdwl} stores the sum of all the ReaxFF potential
energy contributions, with the exception of the Coulombic and charge
equilibration contributions which are stored in the thermo variable
{ecoul}.  The output of these quantities is controlled by the
"thermo"_thermo.html command.

Only a single pair_coeff command is used with the {reax} style which
specifies a ReaxFF potential file with parameters for all needed
elements.  These are mapped to LAMMPS atom types by specifying N
additional arguments after the filename in the pair_coeff command,
where N is the number of LAMMPS atom types:

filename
N indices = mapping of ReaxFF elements to atom types :ul

The specification of the filename and the mapping of LAMMPS atom types
recognized by the ReaxFF is done differently than for other LAMMPS
potentials, due to the non-portable difficulty of passing character
strings (e.g. filename, element names) between C++ and Fortran.

The filename has to be "ffield.reax" and it has to exist in the
directory you are running LAMMPS in.  This means you cannot prepend a
path to the file in the potentials dir.  Rather, you should copy that
file into the directory you are running from.  If you wish to use
another ReaxFF potential file, then name it "ffield.reax" and put in
your running dir.

In the ReaxFF potential file, near the top, is a section that contains
element names, each with a couple dozen numeric parameters.  The
ffield.reax provided with LAMMPS lists 6 elements: C, H, O, N, S, Si.
Think of these as numbered 1 to 6.  Each of the N indices you specify
for the N atom types of LAMMPS atoms must be an integer from 1 to 6.
Atoms with LAMMPS type 1 will be mapped to whatever element you
specify as the first index value, etc.

As an example, if your LAMMPS simulation has 4 atoms types and you
want the 1st two to be C, the 3rd to be N, and the 4th to be H, you
would use the following pair_coeff command:

pair_coeff * * ffield.reax 1 1 4 2 :pre

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[Mixing, shift, table, tail correction, restart, rRESPA info]:

This pair style does not support the "pair_modify"_pair_modify.html
mix, shift, table, and tail options.

This pair style does not write its information to "binary restart
files"_restart.html, since it is stored in potential files.  Thus, you
need to re-specify the pair_style and pair_coeff commands in an input
script that reads a restart file.

This pair style can only be used via the {pair} keyword of the
"run_style respa"_run_style.html command.  It does not support the
{inner}, {middle}, {outer} keywords.

[Restrictions:]

This pair style is part of the "reax" package.  It is only enabled if
LAMMPS was built with that package, which also requires the REAX
library be built and linked with LAMMPS.  See the "Making
LAMMPS"_Section_start.html#2_3 section for more info.

The ffield.reax potential file provided with LAMMPS in the potentials
directory is parameterized for real "units"_units.html.  You can use
the ReaxFF potential with any LAMMPS units, but you would need to
create your own potential file with coefficients listed in the
appropriate units if your simulation doesn't use "real" units.  This
would be somewhat tricky, so contact the LAMMPS authors if you wish to
do this.

[Related commands:]

"pair_coeff"_pair_coeff.html

[Default:] none

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:link(van_Duin_2001)
[(van Duin 2001)] van Duin, Dasgupta, Lorant, Goddard
Journal of Physical Chemistry A, 105, 9396-9409 (2001).

:link(van_Duin_2003)
[(van Duin 2003)] van Duin, Strachan, Stewman, Zhang, Xu, Goddard,
Journal of Physical Chemistry A, 107, 3803-3811 (2003).
