forked from lijiext/lammps
185 lines
6.9 KiB
HTML
185 lines
6.9 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/cuda command
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</H3>
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<H3>pair_style buck/gpu command
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</H3>
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<H3>pair_style buck/omp 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/cut/cuda command
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</H3>
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<H3>pair_style buck/coul/cut/gpu command
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</H3>
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<H3>pair_style buck/coul/cut/omp 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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<H3>pair_style buck/coul/long/cuda command
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</H3>
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<H3>pair_style buck/coul/long/gpu command
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</H3>
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<H3>pair_style buck/coul/long/omp 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>where rho is an ionic-pair dependent length parameter, and Rc is the
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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. For
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<I>buck/coul/long</I>, an additional damping factor is applied to the
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Coulombic term so it can be used in conjunction with the
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<A HREF = "kspace_style.html">kspace_style</A> command and its <I>ewald</I> or <I>pppm</I>
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option. The Coulombic cutoff specified for this style means that
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pairwise interactions within this distance are computed directly;
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interactions outside that distance are computed in reciprocal space.
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</P>
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<P>If one cutoff is specified for the <I>born/coul/cut</I> and
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<I>born/coulk/long</I> styles, it is used for both the A,C and Coulombic
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terms. If two cutoffs are specified, the first is used as the cutoff
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for the A,C terms, and the second is the cutoff for the Coulombic
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term.
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</P>
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<P>Note that these potentials are 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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A,C and Coulombic cutoffs are used. If only one cutoff is specified,
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it is used as the cutoff for both A,C 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 A,C and Coulombic cutoffs for this type pair. You cannot specify
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2 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>Styles with a <I>cuda</I>, <I>gpu</I>, <I>omp</I>, or <I>opt</I> suffix are functionally
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the same as the corresponding style without the suffix. They have
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been optimized to run faster, depending on your available hardware, as
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discussed in <A HREF = "Section_accelerate.html">Section_accelerate</A> of the
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manual. The accelerated styles take the same arguments and should
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produce the same results, except for round-off and precision issues.
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</P>
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<P>These accelerated styles are part of the USER-CUDA, GPU, USER-OMP and OPT
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packages, respectively. They are only enabled if LAMMPS was built with
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those packages. See the <A HREF = "Section_start.html#start_3">Making LAMMPS</A>
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section for more info.
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</P>
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<P>You can specify the accelerated styles explicitly in your input script
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by including their suffix, or you can use the <A HREF = "Section_start.html#start_7">-suffix command-line
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switch</A> when you invoke LAMMPS, or you can
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use the <A HREF = "suffix.html">suffix</A> command in your input script.
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</P>
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<P>See <A HREF = "Section_accelerate.html">Section_accelerate</A> of the manual for
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more instructions on how to use the accelerated styles effectively.
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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>These pair styles do not support mixing. Thus, coefficients for all
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I,J pairs must be specified explicitly.
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</P>
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<P>These styles support the <A HREF = "pair_modify.html">pair_modify</A> shift option
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for the energy of the 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 supports the
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<A HREF = "pair_modify.html">pair_modify</A> table option ti tabulate the
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short-range portion of the long-range Coulombic interaction.
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</P>
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<P>These styles support the pair_modify tail option for adding long-range
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tail corrections to energy and pressure for the A,C terms in the
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pair interaction.
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</P>
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<P>These styles write their information to <A HREF = "restart.html">binary restart
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files</A>, so pair_style and pair_coeff commands do not need
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to be specified in an input script that reads a restart file.
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</P>
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<P>These styles can only be used via the <I>pair</I> keyword of the <A HREF = "run_style.html">run_style
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respa</A> command. They do not support the <I>inner</I>,
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<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 only
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enabled if LAMMPS was built with that package (which it is by
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default). See the <A HREF = "Section_start.html#start_3">Making LAMMPS</A> section
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for 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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