forked from lijiext/lammps
68 lines
2.1 KiB
HTML
68 lines
2.1 KiB
HTML
|
<HTML>
|
||
|
|
<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>
|
||
|
|
</CENTER>
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
<HR>
|
||
|
|
|
||
|
|
<H3>pair_style lj/smooth command
|
||
|
|
</H3>
|
||
|
|
<P><B>Syntax:</B>
|
||
|
|
</P>
|
||
|
|
<PRE>pair_style lj/smooth Rin cutoff
|
||
|
|
</PRE>
|
||
|
|
<UL><LI>Rin = global inner cutoff beyond which force smoothing will be applied (distance units)
|
||
|
|
<LI>cutoff = global cutoff for lj/smooth interactions (distance units)
|
||
|
|
</UL>
|
||
|
|
<P><B>Examples:</B>
|
||
|
|
</P>
|
||
|
|
<PRE>pair_style lj/smooth 8.0 10.0
|
||
|
|
pair_coeff * * 10.0 1.5
|
||
|
|
pair_coeff 1 1 20.0 1.3 7.0 9.0
|
||
|
|
</PRE>
|
||
|
|
<P><B>Description:</B>
|
||
|
|
</P>
|
||
|
|
<P>Style <I>lj/smooth</I> computes a LJ interaction with a force smoothing
|
||
|
|
applied between the inner and outer cutoff.
|
||
|
|
</P>
|
||
|
|
<CENTER><IMG SRC = "Eqs/pair_lj_smooth.jpg">
|
||
|
|
</CENTER>
|
||
|
|
<P>The polynomial coefficients C1, C2, C3, C4 are computed by LAMMPS to
|
||
|
|
cause the force to vary smoothly from Rin to Rc. At Rin the force and
|
||
|
|
its 1st derivative will match the unsmoothed LJ formula. At Rc the
|
||
|
|
force and its 1st derivative will be 0.0. IMPORTANT NOTE: this force
|
||
|
|
smoothing causes the energy to be discontinuous both in its values and
|
||
|
|
1st derivative. This can lead to poor energy conservation. Plot the
|
||
|
|
energy and force resulting from this formula via the
|
||
|
|
<A HREF = "pair_write.html">pair_write</A> command to see the effect.
|
||
|
|
</P>
|
||
|
|
<P>The following coefficients must be defined for each pair of atoms
|
||
|
|
types via the <A HREF = "pair_coeff.html">pair_coeff</A> command as in the examples
|
||
|
|
above, or in the data file or restart files read by the
|
||
|
|
<A HREF = "read_data.html">read_data</A> or <A HREF = "read_restart.html">read_restart</A>
|
||
|
|
commands:
|
||
|
|
</P>
|
||
|
|
<UL><LI>epsilon (energy units)
|
||
|
|
<LI>sigma (distance units)
|
||
|
|
<LI>Rin (distance units)
|
||
|
|
<LI>cutoff (distance units)
|
||
|
|
</UL>
|
||
|
|
<P>The last 2 coefficients are optional. If not specified, the global
|
||
|
|
Rin and cutoff are used. Rin cannot be 0.0. If Rin = cutoff, then no
|
||
|
|
force smoothing is performed for this type pair; the standard LJ
|
||
|
|
formula is used.
|
||
|
|
</P>
|
||
|
|
<P><B>Restrictions:</B> none
|
||
|
|
</P>
|
||
|
|
<P><B>Related commands:</B>
|
||
|
|
</P>
|
||
|
|
<P><A HREF = "pair_coeff.html">pair_coeff</A>
|
||
|
|
</P>
|
||
|
|
<P><B>Default:</B> none
|
||
|
|
</P>
|
||
|
|
</HTML>
|