lammps/doc/pair_reax.txt

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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 interatomic potential energy calculation are
given in the following publications: "(van Duin 2001)"_#van_Duin_2001
and "(van Duin 2003)"_#van_Duin_2003.

ReaxFF parameters for the elements C, H, O, N, S, and Si are provided
in the parameter file ffield.reax in the potentials directory.  For
other elements, or for specific chemical systems, other parameter
files 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.  See the "atom_style"_atom_style.html and
"read_data"_read_data.html commands for details.

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 element names = mapping of ReaxFF elements to atom types :ul

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

pair_coeff * * ffield.reax C C C H :pre

The format of the ReaxFF parameter file is identical to that used by
van Duin and co-workers.

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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.

This pair potential ignores the "newton"_newton.html
settings. Internally, the newton setting is "on" for the force
calculation, but "off" for the neighbor list.

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.

[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).