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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>
</CENTER>
<HR>
<H3>pair_style lj/class2 command
</H3>
<H3>pair_style lj/class2/coul/cut command
</H3>
<H3>pair_style lj/class2/coul/long command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>pair_style style args
</PRE>
<UL><LI>style = <I>lj/class2</I> or <I>lj/class2/coul/cut</I> or <I>lj/class2/coul/long</I>
<LI>args = list of arguments for a particular style
</UL>
<PRE> <I>lj/class2</I> args = cutoff
cutoff = global cutoff for class 2 interactions (distance units)
<I>lj/class2/coul/cut</I> args = cutoff (cutoff2)
cutoff = global cutoff for class 2 (and Coulombic if only 1 arg) (distance units)
cutoff2 = global cutoff for Coulombic (optional) (distance units)
<I>lj/class2/coul/long</I> args = cutoff (cutoff2)
cutoff = global cutoff for class 2 (and Coulombic if only 1 arg) (distance units)
cutoff2 = global cutoff for Coulombic (optional) (distance units)
</PRE>
<P><B>Examples:</B>
</P>
<PRE>pair_style lj/class2 10.0
pair_coeff * * 100.0 2.5
pair_coeff 1 2* 100.0 2.5 9.0
</PRE>
<PRE>pair_style lj/class2/coul/cut 10.0
pair_style lj/class2/coul/cut 10.0 8.0
pair_coeff * * 100.0 3.0
pair_coeff 1 1 100.0 3.5 9.0
pair_coeff 1 1 100.0 3.5 9.0 9.0
</PRE>
<PRE>pair_style lj/class2/coul/long 10.0
pair_style lj/class2/coul/long 10.0 8.0
pair_coeff * * 100.0 3.0
pair_coeff 1 1 100.0 3.5 9.0
</PRE>
<P><B>Description:</B>
</P>
<P>The <I>lj/class2</I> styles compute a 6/9 Lennard-Jones potential given by
</P>
<CENTER><IMG SRC = "Eqs/pair_class2.jpg">
</CENTER>
<P>Rc is the cutoff.
</P>
<P>The <I>lj/class2/coul/cut</I> and <I>lj/class2/coul/long</I> styles add a
Coulombic term as described for the <A HREF = "pair_style_lj.html">lj/cut</A> pair
styles.
</P>
<P>See <A HREF = "#Sun">(Sun)</A> for a description of the COMPASS class2 force field.
</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>cutoff1 (distance units)
<LI>cutoff2 (distance units)
</UL>
<P>The latter 2 coefficients are optional. If not specified, the global
class 2 and Coulombic cutoffs are used. If only one cutoff is
specified, it is used as the cutoff for both class 2 and Coulombic
interactions for this type pair. If both coefficients are specified,
they are used as the class 2 and Coulombic cutoffs for this type pair.
You cannot specify 2 cutoffs for style <I>lj/class2</I>, since it has no
Coulombic terms.
</P>
<P>For <I>lj/class2/coul/long</I> only the class 2 cutoff can be specified
since a Coulombic cutoff cannot be specified for an individual I,J
type pair. All type pairs use the same global Coulombic cutoff
specified in the pair_style command.
</P>
<P><B>Restrictions:</B>
</P>
<P>These styles are part of the "class2" package. They are only enabled
if LAMMPS was built with that package. See the <A HREF = "Section_start.html#2_2">Making
LAMMPS</A> section for more info.
</P>
<P>On some 64-bit machines, compiling with -O3 appears to break the
Coulombic tabling option used by the <I>lj/class2/coul/long</I> style. See
the "Additional build tips" section of the Making LAMMPS documentation
pages for workarounds on this issue.
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "pair_coeff.html">pair_coeff</A>
</P>
<P><B>Default:</B> none
</P>
<HR>
<A NAME = "Sun"></A>
<P><B>(Sun)</B> Sun, J Phys Chem B 102, 7338-7364 (1998).
</P>
</HTML>
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