forked from lijiext/lammps
75 lines
2.7 KiB
HTML
75 lines
2.7 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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<H3>fix rdf command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>fix ID group-ID rdf N file Nbin itype1 jtype1 itype2 jtype2 ...
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</PRE>
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<UL><LI>ID, group-ID are documented in <A HREF = "fix.html">fix</A> command
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<LI>rdf = style name of this fix command
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<LI>N = compute radial distribution function (RDF) every this many timesteps
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<LI>file = filename to write radial distribution funtion info to
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<LI>Nbin = number of RDF bins
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<LI>itypeN = central atom type for RDF pair N
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<LI>jtypeN = distribution atom type for RDF pair N
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</UL>
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<P><B>Examples:</B>
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</P>
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<PRE>fix 1 all rdf 500 rdf.out 100 1 1
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fix 1 fluid rdf 10000 rdf.out 100 1 1 1 2 2 1 2 2
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>Compute the radial distribution function (RDF), also known as g(r),
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and coordination number every N steps. The RDF for each specified
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atom type pair is histogrammed in Nbin bins from distance 0 to Rc,
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where Rc = the maximum force cutoff for any pair of atom types. An
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atom pair only contributes to the RDF if
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</P>
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<UL><LI>both atoms are in the fix group
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<LI>the distance between them is within the maximum force cutoff
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<LI>their interaction is stored in the neighbor list
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</UL>
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<P>Bonded atoms (1-2, 1-3, 1-4 interactions within a molecular topology)
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with a pairwise weighting factor of 0.0 are not included in the RDF;
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pairs with a non-zero weighting factor are included. The weighting
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factor is set by the <A HREF = "special_bonds.html">special_bonds</A> command.
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</P>
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<P>The RDF statistics for each timestep are written to the specified
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file, as are the RDF values averaged over all timesteps.
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</P>
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<P><B>Restart, fix_modify, thermo output, run start/stop, minimize info:</B>
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</P>
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<P>No information about this fix is written to <A HREF = "restart.html">binary restart
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files</A>. None of the <A HREF = "fix_modify.html">fix_modify</A> options
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are relevant to this fix. No quantities calculated by this fix can be
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output by the <A HREF = "thermo_style.html">thermo_style custom</A> command. No
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parameter of this fix can be used with the <I>start/stop</I> keywords of
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the <A HREF = "run.html">run</A> command. This fix is not invoked during <A HREF = "minimize.html">energy
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minimization</A>.
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</P>
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<P><B>Restrictions:</B>
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</P>
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<P>The RDF is not computed for distances longer than the force cutoff,
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since processors (in parallel) don't know atom coordinates for atoms
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further away than that distance. If you want an RDF for larger <I>r</I>,
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you'll need to post-process a dump file.
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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>
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</P>
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<P><B>Default:</B> none
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</P>
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