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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/cuda command
</H3>
<H3>pair_style buck/gpu command
</H3>
<H3>pair_style buck/omp command
</H3>
<H3>pair_style buck/coul/cut command
</H3>
<H3>pair_style buck/coul/cut/cuda command
</H3>
<H3>pair_style buck/coul/cut/gpu command
</H3>
<H3>pair_style buck/coul/cut/omp command
</H3>
<H3>pair_style buck/coul/long command
</H3>
<H3>pair_style buck/coul/long/cuda command
</H3>
<H3>pair_style buck/coul/long/gpu command
</H3>
<H3>pair_style buck/coul/long/omp command
</H3>
<H3>pair_style buck/coul/msm command
</H3>
<H3>pair_style buck/coul/msm/omp 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> or <I>buck/coul/msm</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)
<I>buck/coul/msm</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>
<PRE>pair_style buck/coul/msm 10.0
pair_style buck/coul/msm 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>where rho is an ionic-pair dependent length parameter, and Rc is the
cutoff on both terms.
</P>
<P>The styles with <I>coul/cut</I> or <I>coul/long</I> or <I>coul/msm</I> add a
Coulombic term as described for the <A HREF = "pair_lj.html">lj/cut</A> pair styles.
For <I>buck/coul/long</I> and <I>buc/coul/msm</I>, an additional damping factor
is applied to the Coulombic term so it can be used in conjunction with
the <A HREF = "kspace_style.html">kspace_style</A> command and its <I>ewald</I> or <I>pppm</I>
or <I>msm</I> option. The Coulombic cutoff specified for this style means
that pairwise interactions within this distance are computed directly;
interactions outside that distance are computed in reciprocal space.
</P>
<P>If one cutoff is specified for the <I>born/coul/cut</I> and
<I>born/coul/long</I> and <I>born/coul/msm</I> styles, it is used for both the
A,C and Coulombic terms. If two cutoffs are specified, the first is
used as the cutoff for the A,C terms, and the second is the cutoff for
the Coulombic term.
</P>
<P>Note that these potentials are related to the <A HREF = "pair_born.html">Born-Mayer-Huggins
potential</A>.
</P>
<P>IMPORTANT NOTE: For all these pair styles, the terms with A and C are
always cutoff. The additional Coulombic term can be cutoff or
long-range (no cutoff) depending on whether the style name includes
coul/cut or coul/long or coul/msm. If you wish the C/r^6 term to be
long-range (no cutoff), then see the <A HREF = "pair_buck_long.html">pair_style
buck/long/coul/long</A> command.
</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 second coefficient, rho, must be greater than zero.
</P>
<P>The latter 2 coefficients are optional. If not specified, the global
A,C and Coulombic cutoffs are used. If only one cutoff is specified,
it is used as the cutoff for both A,C and Coulombic interactions for
this type pair. If both coefficients are specified, they are used as
the A,C 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>
<HR>
<P>Styles with a <I>cuda</I>, <I>gpu</I>, <I>omp</I>, or <I>opt</I> suffix are functionally
the same as the corresponding style without the suffix. They have
been optimized to run faster, depending on your available hardware, as
discussed in <A HREF = "Section_accelerate.html">Section_accelerate</A> of the
manual. The accelerated styles take the same arguments and should
produce the same results, except for round-off and precision issues.
</P>
<P>These accelerated styles are part of the USER-CUDA, GPU, USER-OMP and OPT
packages, respectively. They are only enabled if LAMMPS was built with
those packages. See the <A HREF = "Section_start.html#start_3">Making LAMMPS</A>
section for more info.
</P>
<P>You can specify the accelerated styles explicitly in your input script
by including their suffix, or you can use the <A HREF = "Section_start.html#start_7">-suffix command-line
switch</A> when you invoke LAMMPS, or you can
use the <A HREF = "suffix.html">suffix</A> command in your input script.
</P>
<P>See <A HREF = "Section_accelerate.html">Section_accelerate</A> of the manual for
more instructions on how to use the accelerated styles effectively.
</P>
<HR>
<P><B>Mixing, shift, table, tail correction, restart, rRESPA info</B>:
</P>
<P>These pair styles do not support mixing. Thus, coefficients for all
I,J pairs must be specified explicitly.
</P>
<P>These styles support the <A HREF = "pair_modify.html">pair_modify</A> shift option
for the energy of the exp() and 1/r^6 portion of the pair interaction.
</P>
<P>The <I>buck/coul/long</I> pair style supports the
<A HREF = "pair_modify.html">pair_modify</A> table option ti tabulate the
short-range portion of the long-range Coulombic interaction.
</P>
<P>These styles support the pair_modify tail option for adding long-range
tail corrections to energy and pressure for the A,C terms in the
pair interaction.
</P>
<P>These styles write their information to <A HREF = "restart.html">binary restart
files</A>, so pair_style and pair_coeff commands do not need
to be specified in an input script that reads a restart file.
</P>
<P>These styles can only be used via the <I>pair</I> keyword of the <A HREF = "run_style.html">run_style
respa</A> command. They do not support the <I>inner</I>,
<I>middle</I>, <I>outer</I> keywords.
</P>
<P><B>Restrictions:</B>
</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 (which it is by
default). See the <A HREF = "Section_start.html#start_3">Making LAMMPS</A> section
for more info.
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "pair_coeff.html">pair_coeff</A>, <A HREF = "pair_born.html">pair_style born</A>
</P>
<P><B>Default:</B> none
</P>
</HTML>
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