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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/colloid command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>fix ID group-ID wall/colloid style coord A sigma cutoff
</PRE>
<UL><LI>ID, group-ID are documented in <A HREF = "fix.html">fix</A> command
<LI>wall/colloid = 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 (distance units)
<LI>A = Hamaker constant for colloid-wall interactions (energy units)
<LI>sigma = size of constituent LJ particle that integration is done over (distance units)
<LI>cutoff = distance from wall at which wall-particle interaction is cut off (distance units)
</UL>
<P><B>Examples:</B>
</P>
<PRE>fix wallhi all wall/colloid xhi 10.0 20.0 1.0 2.5
fix leftwall all wall/colloid zlo 0.0 10.0 1.0 0.858
</PRE>
<P><B>Description:</B>
</P>
<P>Bound the simulation domain on one of its faces with a wall of
Lennard-Jones particles that interacts with finite-size colloidal
particles in the group. The energy E of wall-colloid interactions is
given by an integrated form of the <A HREF = "pair_colloid.html">pair_style
colloid</A> potential
</P>
<CENTER><IMG SRC = "Eqs/fix_wall_colloid.jpg">
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<P>where A is the specified Hamaker constant for the colloid-wall
interaction, <I>r</I> is the distance from the center of the particle to
the wall <I>coord</I>, <I>R</I> is the radius of the colloid particle, <I>D</I> is
the distance from the surface of the colloid particle to the wall
(r-R), sigma is the size of the constituent LJ particle integrated
over as described below, and Rc is the cutoff value specified in the
fix command and is the distance from the particle center to the wall.
</P>
<P>This colloid/wall interaction is derived by integrating over both the
constituent LJ particles in the colloid particle and a 3d half-lattice
of Lennard-Jones 12-6 particles in the wall.
</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 colloid wall must be non-periodic.
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "fix_wall_lj93.html">fix wall/lj93</A>, <A HREF = "pair_colloid.html">pair_style
colloid</A>
</P>
<P><B>Default:</B> none
</P>
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