2009-02-07 00:12:07 +08:00
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<CENTER><A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</A> - <A HREF = "Manual.html">LAMMPS Documentation</A> - <A HREF = "Section_commands.html#comm">LAMMPS Commands</A>
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<HR>
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<H3>pair_style reax command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>pair_style reax hbcut precision
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</PRE>
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<UL><LI>hbcut = hydrogen-bond cutoff (distance units)
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<LI>precision = precision for charge equilibration
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</UL>
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<P><B>Examples:</B>
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</P>
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<PRE>pair_style reax
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pair_style reax 10.0 1.0e-5
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pair_coeff * * ffield.reax C H O N
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>The pair style computes the ReaxFF potential of van Duin, Goddard and
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co-workers. ReaxFF uses distance-dependent bond-order functions to
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represent the contributions of chemical bonding to the potential
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energy. Details of the interatomic potential energy calculation are
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given in the following publications: <A HREF = "#van_Duin_2001">(van Duin 2001)</A>
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and <A HREF = "#van_Duin_2003">(van Duin 2003)</A>.
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</P>
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<P>ReaxFF parameters for the elements C, H, O, N, S, and Si are provided
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in the parameter file ffield.reax in the potentials directory. For
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other elements, or for specific chemical systems, other parameter
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files may be available elsewhere.
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2009-02-07 00:12:07 +08:00
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</P>
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<P>The <I>hbcut</I> and <I>precision</I> settings are optional arguments. If
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neither is provided, default settings are used: <I>hbcut</I> = 10 (which is
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Angstroms in real units) and <I>precision</I> = 1.0e-6 (one part in 10^6).
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If you wish to override either of these defaults, then both settings
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must be specified.
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2009-02-07 00:12:07 +08:00
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</P>
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<P>Use of this pair style requires that a charge be defined for every
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atom. See the <A HREF = "atom_style.html">atom_style</A> and
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<A HREF = "read_data.html">read_data</A> commands for details.
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</P>
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<P>The thermo variable <I>evdwl</I> stores the sum of all the ReaxFF potential
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energy contributions, with the exception of the Coulombic and charge
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equilibration contributions which are stored in the thermo variable
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<I>ecoul</I>. The output of these quantities is controlled by the
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<A HREF = "thermo.html">thermo</A> command.
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</P>
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<P>Only a single pair_coeff command is used with the <I>reax</I> style which
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specifies a ReaxFF potential file with parameters for all needed
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elements. These are mapped to LAMMPS atom types by specifying N
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additional arguments after the filename in the pair_coeff command,
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where N is the number of LAMMPS atom types:
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</P>
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<UL><LI>filename
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<LI>N element names = mapping of ReaxFF elements to atom types
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</UL>
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<P>As an example, if your LAMMPS simulation has 4 atoms types and you
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want the 1st 3 to be C, and the 4th to be H, you would use the
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following pair_coeff command:
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</P>
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<PRE>pair_coeff * * ffield.reax C C C H
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</PRE>
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<P>The format of the ReaxFF parameter file is identical to that used by
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van Duin and co-workers.
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</P>
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2009-02-07 00:12:07 +08:00
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<HR>
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<P><B>Mixing, shift, table, tail correction, restart, rRESPA info</B>:
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</P>
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<P>This pair style does not support the <A HREF = "pair_modify.html">pair_modify</A>
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mix, shift, table, and tail options.
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</P>
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<P>This pair style does not write its information to <A HREF = "restart.html">binary restart
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files</A>, since it is stored in potential files. Thus, you
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need to re-specify the pair_style and pair_coeff commands in an input
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script that reads a restart file.
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</P>
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<P>This pair style can only be used via the <I>pair</I> keyword of the
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<A HREF = "run_style.html">run_style respa</A> command. It does not support the
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<I>inner</I>, <I>middle</I>, <I>outer</I> keywords.
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</P>
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<P><B>Restrictions:</B>
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</P>
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<P>This pair style is part of the "reax" package. It is only enabled if
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LAMMPS was built with that package, which also requires the REAX
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library be built and linked with LAMMPS. See the <A HREF = "Section_start.html#2_3">Making
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LAMMPS</A> section for more info.
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2009-02-07 00:12:07 +08:00
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</P>
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2009-02-07 00:40:44 +08:00
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<P>This pair potential ignores the <A HREF = "newton.html">newton</A>
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settings. Internally, the newton setting is "on" for the force
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calculation, but "off" for the neighbor list.
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2009-02-07 00:12:07 +08:00
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</P>
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2009-02-07 00:40:44 +08:00
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<P>The ffield.reax potential file provided with LAMMPS in the potentials
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directory is parameterized for real <A HREF = "units.html">units</A>. You can use
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the ReaxFF potential with any LAMMPS units, but you would need to
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create your own potential file with coefficients listed in the
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appropriate units if your simulation doesn't use "real" units.
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2009-02-07 00:12:07 +08:00
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</P>
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<P><B>Related commands:</B>
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</P>
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<P><A HREF = "pair_coeff.html">pair_coeff</A>
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</P>
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<P><B>Default:</B> none
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</P>
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<HR>
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<A NAME = "van_Duin_2001"></A>
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<P><B>(van Duin 2001)</B> van Duin, Dasgupta, Lorant, Goddard
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Journal of Physical Chemistry A, 105, 9396-9409 (2001).
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</P>
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<A NAME = "van_Duin_2003"></A>
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<P><B>(van Duin 2003)</B> van Duin, Strachan, Stewman, Zhang, Xu, Goddard,
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Journal of Physical Chemistry A, 107, 3803-3811 (2003).
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</P>
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</HTML>
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