forked from lijiext/lammps
66 lines
1.9 KiB
HTML
66 lines
1.9 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 soft 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 soft cutoff
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</PRE>
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<UL><LI>cutoff = global cutoff for soft interactions (distance units)
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</UL>
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<P><B>Examples:</B>
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</P>
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<PRE>pair_style soft 2.5
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pair_coeff * * 0.0 60.0
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pair_coeff 1 1 0.0 60.0 3.0
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>Style <I>soft</I> computes pairwise interactions with the formula
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</P>
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<CENTER><IMG SRC = "Eqs/pair_soft.jpg">
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</CENTER>
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<P>It is useful for pushing apart overlapping atoms, since it does not
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blow up as r goes to 0. A is a pre-factor that varies in time from
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the start to the end of the run. The <A HREF = "run.html">run</A> command documents
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how to make the ramping take place across multiple runs. Rc is the
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cutoff.
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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>Astart (energy units)
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<LI>Astop (energy units)
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<LI>cutoff (distance units)
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</UL>
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<P>Astart and Astop are the values of the prefactor at the start and end
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of the next run. At intermediate times the value of A will be ramped
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between these 2 values. Note that before performing a 2nd run, you
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will want to adjust the values of Astart and Astop for all type pairs,
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or switch to a new pair style.
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</P>
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<P>The last coefficient is optional. If not specified, the global soft
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cutoff is used.
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</P>
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<P><B>Restrictions:</B> none
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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>
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</P>
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<P><B>Default:</B> none
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</P>
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