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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>
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<H3>fix wall/lj93 command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>fix ID group-ID wall/lj93 style coord epsilon sigma cutoff
</PRE>
<UL><LI>ID, group-ID are documented in <A HREF = "fix.html">fix</A> command
<LI>wall/lj93 = style name of this fix command
<LI>style = <I>xlo</I> or <I>xhi</I> or <I>ylo</I> or <I>yhi</I> or <I>zlo</I> or <I>zhi</I>
<LI>coord = position of wall
<LI>epsilon = Lennard-Jones epsilon for wall-particle interaction
<LI>sigma = Lennard-Jones sigma for wall-particle interaction
<LI>cutoff = distance from wall at which wall-particle interaction is cut off
</UL>
<P><B>Examples:</B>
</P>
<PRE>fix wallhi all wall/lj93 xhi 10.0 1.0 1.0 2.5
</PRE>
<P><B>Description:</B>
</P>
<P>Bound the simulation domain with a Lennard-Jones wall that encloses
the atoms. The energy E of a wall-particle interactions is given by
the 9-3 potential
</P>
<CENTER><IMG SRC = "Eqs/fix_wall_lj93.jpg">
</CENTER>
<P>where <I>r</I> is the distance from the particle to the wall <I>coord</I>, and
epsilon and sigma are the usual LJ parameters. Rc is the cutoff value
specified in the command. This interaction is derived by integrating
over a 3d half-lattice of Lennard-Jones 12-6 particles. A harder,
more repulsive wall interaction can be computed by using the <A HREF = "fix_wall_lj126.html">fix
wall/lj126</A> command.
</P>
<P>The wall potential is shifted so that the energy of a wall-particle
interaction is 0.0 at the cutoff distance.
</P>
<P><B>Restart, fix_modify, output, run start/stop, minimize info:</B>
</P>
<P>No information about this fix is written to <A HREF = "restart.html">binary restart
files</A>.
</P>
<P>The <A HREF = "fix_modify.html">fix_modify</A> <I>energy</I> option is supported by this
fix to add the energy of interaction between atoms and the wall to the
system's potential energy as part of <A HREF = "thermo_style.html">thermodynamic
output</A>.
</P>
<P>This fix computes a scalar energy and a 3-vector of forces (on the
wall), which can be accessed by various <A HREF = "Section_howto.html#4_15">output
commands</A>. The scalar and vector values
calculated by this fix are "extensive", meaning they scale with the
number of atoms in the simulation.
</P>
<P>No parameter of this fix can be used with the <I>start/stop</I> keywords of
the <A HREF = "run.html">run</A> command.
</P>
<P>The forces due to this fix are imposed during an energy minimization,
invoked by the <A HREF = "minimize.html">minimize</A> command.
</P>
<P>IMPORTANT NOTE: If you want the atom/wall interaction energy to be
included in the total potential energy of the system (the quantity
being minimized), you MUST enable the <A HREF = "fix_modify.html">fix_modify</A>
<I>energy</I> option for this fix.
</P>
<P><B>Restrictions:</B>
</P>
<P>Any dimension (xyz) that has a LJ 9/3 wall must be non-periodic.
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "fix_wall_reflect.html">fix wall/reflect</A>, <A HREF = "fix_wall_lj126.html">fix
wall/lj126</A>
</P>
<P><B>Default:</B> none
</P>
</HTML>
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