forked from lijiext/lammps
113 lines
3.9 KiB
HTML
113 lines
3.9 KiB
HTML
<HTML>
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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>
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<HR>
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<H3>fix wall/lj93 command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>fix ID group-ID wall/lj93 style coord epsilon sigma cutoff keyword values ...
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</PRE>
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<UL><LI>ID, group-ID are documented in <A HREF = "fix.html">fix</A> command
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<LI>wall/lj93 = style name of this fix command
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<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>
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<LI>coord = position of wall
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<LI>epsilon = Lennard-Jones epsilon for wall-particle interaction
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<LI>sigma = Lennard-Jones sigma for wall-particle interaction
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<LI>cutoff = distance from wall at which wall-particle interaction is cut off (distance units)
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<LI>one or more keyword/value pairs may be appended
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<LI>keyword = <I>vel</I>
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<PRE> <I>vel</I> args = v
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v = velocity of wall in perpendicular direction (velocity units)
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</PRE>
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</UL>
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<P><B>Examples:</B>
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</P>
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<PRE>fix wallhi all wall/lj93 xhi 10.0 1.0 1.0 2.5
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fix leftwall all wall/lj93 zlo 0.0 1.0 1.0 0.858 vel 1.0
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>Bound the simulation domain on one of its faces with a Lennard-Jones
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wall that interacts with the atoms in the group. The energy E of
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wall-particle interactions is given by the 9-3 potential
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</P>
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<CENTER><IMG SRC = "Eqs/fix_wall_lj93.jpg">
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</CENTER>
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<P>where <I>r</I> is the distance from the particle to the wall <I>coord</I>, and
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epsilon and sigma are the usual LJ parameters. Rc is the cutoff value
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specified in the command. This interaction is derived by integrating
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over a 3d half-lattice of Lennard-Jones 12-6 particles. A harder,
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more repulsive wall interaction can be computed by using the <A HREF = "fix_wall_lj126.html">fix
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wall/lj126</A> command.
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</P>
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<P>The wall potential is shifted so that the energy of a wall-particle
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interaction is 0.0 at the cutoff distance.
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</P>
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<P>If the <I>vel</I> keyword is specified, the position of wall will move
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during the simulation, based on its initial position (coord) and the
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specified velocity (vel). <I>Xlo</I> or <I>xhi</I> walls move in the x
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direction with whatever sign you give the <I>v</I> argument. Ditto for <I>y</I>
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and <I>z</I> walls. Note that if you do multiple runs, the initial
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position of the wall does not change, so it will continue to move at
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the specified velocity.
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</P>
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<P><B>Restart, fix_modify, output, run start/stop, minimize info:</B>
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</P>
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<P>No information about this fix is written to <A HREF = "restart.html">binary restart
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files</A>.
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</P>
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<P>The <A HREF = "fix_modify.html">fix_modify</A> <I>energy</I> option is supported by this
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fix to add the energy of interaction between atoms and the wall to the
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system's potential energy as part of <A HREF = "thermo_style.html">thermodynamic
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output</A>.
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</P>
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<P>This fix computes a scalar energy and a 3-vector of forces (on the
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wall), which can be accessed by various <A HREF = "Section_howto.html#4_15">output
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commands</A>. The scalar and vector values
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calculated by this fix are "extensive", meaning they scale with the
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number of atoms in the simulation.
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</P>
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<P>No parameter of this fix can be used with the <I>start/stop</I> keywords of
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the <A HREF = "run.html">run</A> command.
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</P>
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<P>The forces due to this fix are imposed during an energy minimization,
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invoked by the <A HREF = "minimize.html">minimize</A> command.
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</P>
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<P>IMPORTANT NOTE: If you want the atom/wall interaction energy to be
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included in the total potential energy of the system (the quantity
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being minimized), you MUST enable the <A HREF = "fix_modify.html">fix_modify</A>
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<I>energy</I> option for this fix.
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</P>
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<P><B>Restrictions:</B>
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</P>
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<P>Any dimension (xyz) that has a LJ 9/3 wall must be non-periodic.
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</P>
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<P><B>Related commands:</B>
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</P>
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<P><A HREF = "fix_wall_reflect.html">fix wall/reflect</A>, <A HREF = "fix_wall_lj126.html">fix
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wall/lj126</A>
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</P>
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<P><B>Default:</B>
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</P>
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<P>The option defaults are vel = 0.
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</P>
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</HTML>
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