forked from lijiext/lammps
95 lines
3.7 KiB
HTML
95 lines
3.7 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/colloid 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/colloid style coord A sigma cutoff
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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/colloid = 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 (distance units)
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<LI>A = Hamaker constant for colloid-wall interactions (energy units)
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<LI>sigma = size of constituent LJ particle that integration is done over (distance units)
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<LI>cutoff = distance from wall at which wall-particle interaction is cut off (distance units)
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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/colloid xhi 10.0 20.0 1.0 2.5
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fix leftwall all wall/colloid zlo 0.0 10.0 1.0 0.858
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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 wall of
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Lennard-Jones particles that interacts with finite-size colloidal
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particles in the group. The energy E of wall-colloid interactions is
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given by an integrated form of the <A HREF = "pair_colloid.html">pair_style
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colloid</A> potential
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</P>
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<CENTER><IMG SRC = "Eqs/fix_wall_colloid.jpg">
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</CENTER>
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<P>where A is the specified Hamaker constant for the colloid-wall
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interaction, <I>r</I> is the distance from the center of the particle to
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the wall <I>coord</I>, <I>R</I> is the radius of the colloid particle, <I>D</I> is
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the distance from the surface of the colloid particle to the wall
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(r-R), sigma is the size of the constituent LJ particle integrated
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over as described below, and Rc is the cutoff value specified in the
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fix command and is the distance from the particle center to the wall.
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</P>
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<P>This colloid/wall interaction is derived by integrating over both the
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constituent LJ particles in the colloid particle and a 3d half-lattice
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of Lennard-Jones 12-6 particles in the wall.
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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><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 colloid 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_lj93.html">fix wall/lj93</A>, <A HREF = "pair_colloid.html">pair_style
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colloid</A>
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</P>
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<P><B>Default:</B> none
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</P>
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</HTML>
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