forked from lijiext/lammps
115 lines
4.1 KiB
HTML
115 lines
4.1 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>fix wall/lj93 command
|
|
</H3>
|
|
<P><B>Syntax:</B>
|
|
</P>
|
|
<PRE>fix ID group-ID wall/lj93 style coord epsilon sigma cutoff keyword values ...
|
|
</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 (distance units)
|
|
|
|
<LI>one or more keyword/value pairs may be appended
|
|
|
|
<LI>keyword = <I>vel</I>
|
|
|
|
<PRE> <I>vel</I> args = v
|
|
v = velocity of wall in perpendicular direction (velocity units)
|
|
</PRE>
|
|
|
|
</UL>
|
|
<P><B>Examples:</B>
|
|
</P>
|
|
<PRE>fix wallhi all wall/lj93 xhi 10.0 1.0 1.0 2.5
|
|
fix leftwall all wall/lj93 zlo 0.0 1.0 1.0 0.858 vel 1.0
|
|
</PRE>
|
|
<P><B>Description:</B>
|
|
</P>
|
|
<P>Bound the simulation domain on one of its faces with a Lennard-Jones
|
|
wall that interacts with the atoms in the group. The energy E of
|
|
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>If the <I>vel</I> keyword is specified, the position of wall will move
|
|
during the simulation, based on its initial position (coord), the
|
|
specified velocity (vel), and the time elapsed since the beginning of
|
|
the simulation. <I>Xlo</I> or <I>xhi</I> walls move in the x direction with
|
|
whatever sign you give the <I>v</I> argument. Ditto for <I>y</I> and <I>z</I> walls.
|
|
See the note below about making the wall move continuously across
|
|
multiple runs.
|
|
</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>This fix can change the position of the wall, due to the <I>vel</I>
|
|
keyword, continuously over multiple runs, using the <I>start</I> and <I>stop</I>
|
|
keywords of the <A HREF = "run.html">run</A> command. If you do not do this, the
|
|
wall position will be reset to <I>coord</I> at the beginning of each run.
|
|
</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>
|
|
</P>
|
|
<P>The option defaults are vel = 0.
|
|
</P>
|
|
</HTML>
|