forked from lijiext/lammps
84 lines
3.2 KiB
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84 lines
3.2 KiB
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<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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<H3>pair_write 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_write itype jtype N style inner outer file keyword Qi Qj
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</PRE>
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<UL><LI>itype,jtype = 2 atom types
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<LI>N = # of values
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<LI>style = <I>r</I> or <I>rsq</I> or <I>bitmap</I>
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<LI>inner,outer = inner and outer cutoff (distance units)
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<LI>file = name of file to write values to
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<LI>keyword = section name in file for this set of tabulated values
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<LI>Qi,Qj = 2 atom charges (charge units) (optional)
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</UL>
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<P><B>Examples:</B>
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</P>
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<PRE>pair_write 1 3 500 r 1.0 10.0 table.txt LJ
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pair_write 1 1 1000 rsq 2.0 8.0 table.txt Yukawa_1_1 -0.5 0.5
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>Write energy and force values to a file as a function of distance for
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the currently defined pair potential. This is useful for plotting the
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potential function or otherwise debugging its values. If the file
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already exists, the table of values is appended to the end of the file
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to allow multiple tables of energy and force to be included in one
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file.
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</P>
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<P>The energy and force values are computed at distances from inner to
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outer for 2 interacting atoms of type itype and jtype, using the
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appropriate <A HREF = "pair_coeff.html">pair_coeff</A> coefficients. If the style
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is <I>r</I>, then N distances are used, evenly spaced in r; if the style is
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<I>rsq</I>, N distances are used, evenly spaced in r^2.
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</P>
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<P>For example, for N = 7, style = <I>r</I>, inner = 1.0, and outer = 4.0,
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values are computed at r = 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0.
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</P>
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<P>If the style is <I>bitmap</I>, then 2^N values are written to the file in a
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format and order consistent with how they are read in by the
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<A HREF = "pair_coeff.html">pair_coeff</A> command for pair style <I>table</I>. For
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reasonable accuracy in a bitmapped table, choose N >= 12, an <I>inner</I>
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value that is smaller than the distance of closest approach of 2
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atoms, and an <I>outer</I> value <= cutoff of the potential.
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</P>
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<P>If the pair potential is computed between charged atoms, the charges
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of the pair of interacting atoms can optionally be specified. If not
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specified, values of Qi = Qj = 1.0 are used.
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</P>
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<P>The file is written in the format used as input for the
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<A HREF = "pair_style.html">pair_style</A> <I>table</I> option with <I>keyword</I> as the
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section name. Each line written to the file lists an index number
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(1-N), a distance (in distance units), an energy (in energy units),
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and a force (in force units).
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</P>
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<P><B>Restrictions:</B>
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</P>
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<P>All force field coefficients for pair and other kinds of interactions
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must be set before this command can be invoked.
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</P>
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<P>Due to how the pairwise force is computed, an inner value > 0.0 must
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be specified even if the potential has a finite value at r = 0.0.
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</P>
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<P>For EAM potentials, the pair_write command only tabulates the
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pairwise portion of the potential, not the embedding portion.
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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_style.html">pair_style</A>, <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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</HTML>
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