forked from lijiext/lammps
133 lines
4.7 KiB
HTML
133 lines
4.7 KiB
HTML
<HTML>
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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 buck command
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</H3>
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<H3>pair_style buck/coul/cut command
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</H3>
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<H3>pair_style buck/coul/long 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 style args
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</PRE>
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<UL><LI>style = <I>buck</I> or <I>buck/coul/cut</I> or <I>buck/coul/long</I>
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<LI>args = list of arguments for a particular style
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</UL>
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<PRE> <I>buck</I> args = cutoff
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cutoff = global cutoff for Buckingham interactions (distance units)
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<I>buck/coul/cut</I> args = cutoff (cutoff2)
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cutoff = global cutoff for Buckingham (and Coulombic if only 1 arg) (distance units)
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cutoff2 = global cutoff for Coulombic (optional) (distance units)
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<I>buck/coul/long</I> args = cutoff (cutoff2)
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cutoff = global cutoff for Buckingham (and Coulombic if only 1 arg) (distance units)
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cutoff2 = global cutoff for Coulombic (optional) (distance units)
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</PRE>
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<P><B>Examples:</B>
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</P>
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<PRE>pair_style buck 2.5
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pair_coeff * * 100.0 1.5 200.0
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pair_coeff * * 100.0 1.5 200.0 3.0
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</PRE>
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<PRE>pair_style buck/coul/cut 10.0
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pair_style buck/coul/cut 10.0 8.0
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pair_coeff * * 100.0 1.5 200.0
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pair_coeff 1 1 100.0 1.5 200.0 9.0
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pair_coeff 1 1 100.0 1.5 200.0 9.0 8.0
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</PRE>
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<PRE>pair_style buck/coul/long 10.0
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pair_style buck/coul/long 10.0 8.0
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pair_coeff * * 100.0 1.5 200.0
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pair_coeff 1 1 100.0 1.5 200.0 9.0
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>The <I>buck</I> style computes a Buckingham potential (exp/6 instead of
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Lennard-Jones 12/6) given by
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</P>
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<CENTER><IMG SRC = "Eqs/pair_buck.jpg">
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</CENTER>
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<P>Rc is the cutoff.
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</P>
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<P>The <I>buck/coul/cut</I> and <I>buck/coul/long</I> styles add a Coulombic term
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as described for the <A HREF = "pair_lj.html">lj/cut</A> pair styles.
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</P>
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<P>Note that this potential is related to the <A HREF = "pair_born.html">Born-Mayer-Huggins
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potential</A>.
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</P>
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<P>The following coefficients must be defined for each pair of atoms
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types via the <A HREF = "pair_coeff.html">pair_coeff</A> command as in the examples
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above, or in the data file or restart files read by the
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<A HREF = "read_data.html">read_data</A> or <A HREF = "read_restart.html">read_restart</A>
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commands:
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</P>
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<UL><LI>A (energy units)
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<LI>rho (distance units)
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<LI>C (energy-distance^6 units)
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<LI>cutoff (distance units)
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<LI>cutoff2 (distance units)
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</UL>
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<P>The second coefficient, rho, must be greater than zero.
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</P>
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<P>The latter 2 coefficients are optional. If not specified, the global
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LJ and Coulombic cutoffs are used. If only one cutoff is specified,
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it is used as the cutoff for both LJ and Coulombic interactions for
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this type pair. If both coefficients are specified, they are used as
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the LJ and Coulombic cutoffs for this type pair. You cannot specify 2
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cutoffs for style <I>buck</I>, since it has no Coulombic terms.
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</P>
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<P>For <I>buck/coul/long</I> only the LJ cutoff can be specified since a
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Coulombic cutoff cannot be specified for an individual I,J type pair.
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All type pairs use the same global Coulombic cutoff specified in the
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pair_style command.
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</P>
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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>None of the Buckingham pair styles support mixing. Thus, coefficients
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for all I,J pairs must be specified explicitly.
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</P>
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<P>All of the Buckingham pair styles support the
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<A HREF = "pair_modify.html">pair_modify</A> shift option for the energy of the
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exp() and 1/r^6 portion of the pair interaction.
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</P>
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<P>The <I>buck/coul/long</I> pair style does not support the
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<A HREF = "pair_modify.html">pair_modify</A> table option since a tabulation
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capability has not yet been added to this potential.
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</P>
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<P>None of the Buckingham pair styles support the
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<A HREF = "pair_modify.html">pair_modify</A> tail option for adding long-range tail
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corrections to energy and pressure.
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</P>
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<P>All of the Buckingham pair styles write their information to <A HREF = "restart.html">binary
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restart files</A>, so pair_style and pair_coeff commands do
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not need to be specified in an input script that reads a restart file.
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</P>
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<P>All of the Buckingham pair styles can only be used via the <I>pair</I>
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keyword of the <A HREF = "run_style.html">run_style respa</A> command. They do not
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support the <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>The <I>buck/coul/long</I> style is part of the "kspace" package. It is
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only enabled if LAMMPS was built with that package (which it is by
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default). See the <A HREF = "Section_start.html#2_3">Making LAMMPS</A> section for
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more info.
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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>, <A HREF = "pair_born.html">pair_style born</A>
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</P>
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<P><B>Default:</B> none
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</P>
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</HTML>
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