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<HTML>
<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>
</CENTER>
<HR>
<H3>pair_style buck command
</H3>
<H3>pair_style buck/coul/cut command
</H3>
<H3>pair_style buck/coul/long command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>pair_style style args
</PRE>
<UL><LI>style = <I>buck</I> or <I>buck/coul/cut</I> or <I>buck/coul/long</I>
<LI>args = list of arguments for a particular style
</UL>
<PRE> <I>buck</I> args = cutoff
cutoff = global cutoff for Buckingham interactions (distance units)
<I>buck/coul/cut</I> args = cutoff (cutoff2)
cutoff = global cutoff for Buckingham (and Coulombic if only 1 arg) (distance units)
cutoff2 = global cutoff for Coulombic (optional) (distance units)
<I>buck/coul/long</I> args = cutoff (cutoff2)
cutoff = global cutoff for Buckingham (and Coulombic if only 1 arg) (distance units)
cutoff2 = global cutoff for Coulombic (optional) (distance units)
</PRE>
<P><B>Examples:</B>
</P>
<PRE>pair_style buck 2.5
pair_coeff * * 100.0 1.5 200.0
pair_coeff * * 100.0 1.5 200.0 3.0
</PRE>
<PRE>pair_style buck/coul/cut 10.0
pair_style buck/coul/cut 10.0 8.0
pair_coeff * * 100.0 1.5 200.0
pair_coeff 1 1 100.0 1.5 200.0 9.0
pair_coeff 1 1 100.0 1.5 200.0 9.0 8.0
</PRE>
<PRE>pair_style buck/coul/long 10.0
pair_style buck/coul/long 10.0 8.0
pair_coeff * * 100.0 1.5 200.0
pair_coeff 1 1 100.0 1.5 200.0 9.0
</PRE>
<P><B>Description:</B>
</P>
<P>The <I>buck</I> style computes a Buckingham potential (exp/6 instead of
Lennard-Jones 12/6) given by
</P>
<CENTER><IMG SRC = "Eqs/pair_buck.jpg">
</CENTER>
<P>Rc is the cutoff.
</P>
<P>The <I>buck/coul/cut</I> and <I>buck/coul/long</I> styles add a Coulombic term
as described for the <A HREF = "pair_style_lj.html">lj/cut</A> pair styles.
</P>
<P>The following coefficients must be defined for each pair of atoms
types via the <A HREF = "pair_coeff.html">pair_coeff</A> command as in the examples
above, or in the data file or restart files read by the
<A HREF = "read_data.html">read_data</A> or <A HREF = "read_restart.html">read_restart</A>
commands:
</P>
<UL><LI>A (energy units)
<LI>rho (distance units)
<LI>C (energy-distance^6 units)
<LI>cutoff (distance units)
<LI>cutoff2 (distance units)
</UL>
<P>The latter 2 coefficients are optional. If not specified, the global
LJ and Coulombic cutoffs are used. If only one cutoff is specified,
it is used as the cutoff for both LJ and Coulombic interactions for
this type pair. If both coefficients are specified, they are used as
the LJ and Coulombic cutoffs for this type pair. You cannot specify 2
cutoffs for style <I>buck</I>, since it has no Coulombic terms.
</P>
<P>For <I>buck/coul/long</I> only the LJ cutoff can be specified since a
Coulombic cutoff cannot be specified for an individual I,J type pair.
All type pairs use the same global Coulombic cutoff specified in the
pair_style command.
</P>
<P><B>Restrictions:</B>
</P>
<P>The <I>buck</I> potentials do not support the
<A HREF = "pair_modify.hmtl">pair_modify</A> <I>mix</I> option. Coefficients for all i,j
pairs must be specified explicitly.
</P>
<P>The <I>buck/coul/long</I> style is part of the "kspace" package. It is
only enabled if LAMMPS was built with that package. See the <A HREF = "Section_start.html#2_2">Making
LAMMPS</A> section for more info.
</P>
<P>On some 64-bit machines, compiling with -O3 appears to break the
Coulombic tabling option used by the <I>buck/coul/long</I> style. See
the "Additional build tips" section of the Making LAMMPS documentation
pages for workarounds on this issue.
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "pair_coeff.html">pair_coeff</A>
</P>
<P><B>Default:</B> none
</P>
</HTML>
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