2006-09-22 00:22:34 +08:00
|
|
|
<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 addforce command
|
|
|
|
|
</H3>
|
|
|
|
|
<P><B>Syntax:</B>
|
|
|
|
|
</P>
|
2009-08-09 06:03:37 +08:00
|
|
|
<PRE>fix ID group-ID addforce fx fy fz keyword value ...
|
2006-09-22 00:22:34 +08:00
|
|
|
</PRE>
|
2009-08-09 06:03:37 +08:00
|
|
|
<UL><LI>ID, group-ID are documented in <A HREF = "fix.html">fix</A> command
|
|
|
|
|
|
|
|
|
|
<LI>addforce = style name of this fix command
|
|
|
|
|
|
2006-09-22 00:22:34 +08:00
|
|
|
<LI>fx,fy,fz = force component values (force units)
|
2009-08-09 06:03:37 +08:00
|
|
|
|
|
|
|
|
<LI>zero or more keyword/value pairs may be appended to args
|
|
|
|
|
|
|
|
|
|
<LI>keyword = <I>region</I>
|
|
|
|
|
|
|
|
|
|
<PRE> <I>region</I> value = region-ID
|
|
|
|
|
region-ID = ID of region atoms must be in to have added force
|
|
|
|
|
</PRE>
|
|
|
|
|
|
2006-09-22 00:22:34 +08:00
|
|
|
</UL>
|
|
|
|
|
<P><B>Examples:</B>
|
|
|
|
|
</P>
|
|
|
|
|
<PRE>fix kick flow addforce 1.0 0.0 0.0
|
|
|
|
|
</PRE>
|
|
|
|
|
<P><B>Description:</B>
|
|
|
|
|
</P>
|
|
|
|
|
<P>Add fx,fy,fz to the corresponding component of force for each atom in
|
|
|
|
|
the group. This command can be used to give an additional push to
|
|
|
|
|
atoms in a simulation, such as for a simulation of Poiseuille flow in
|
|
|
|
|
a channel.
|
|
|
|
|
</P>
|
2009-08-09 06:03:37 +08:00
|
|
|
<P>If the <I>region</I> keyword is used, the atom must also be in the
|
|
|
|
|
specified geometric <A HREF = "region.html">region</A> in order to have force added
|
|
|
|
|
to it.
|
|
|
|
|
</P>
|
2007-10-11 06:28:11 +08:00
|
|
|
<P><B>Restart, fix_modify, output, run start/stop, minimize info:</B>
|
2007-06-26 08:03:39 +08:00
|
|
|
</P>
|
|
|
|
|
<P>No information about this fix is written to <A HREF = "restart.html">binary restart
|
2008-08-01 23:10:00 +08:00
|
|
|
files</A>.
|
2008-03-18 04:49:34 +08:00
|
|
|
</P>
|
2008-08-01 23:10:00 +08:00
|
|
|
<P>The <A HREF = "fix_modify.html">fix_modify</A> <I>energy</I> option is supported by this
|
|
|
|
|
fix to add the potential "energy" inferred by the added force to the
|
|
|
|
|
system's potential energy as part of <A HREF = "thermo_style.html">thermodynamic
|
|
|
|
|
output</A>. This is a fictitious quantity but is
|
|
|
|
|
needed so that the <A HREF = "minimize.html">minimize</A> command can include the
|
|
|
|
|
forces added by this fix in a consistent manner. I.e. there is a
|
|
|
|
|
decrease in potential energy when atoms move in the direction of the
|
|
|
|
|
added force.
|
|
|
|
|
</P>
|
|
|
|
|
<P>This fix computes a scalar and a 3-vector of forces, which can be
|
|
|
|
|
accessed by various <A HREF = "Section_howto.html#4_15">output commands</A>. The
|
|
|
|
|
scalar is the potential energy discussed above. The vector is the
|
|
|
|
|
total force on the group of atoms before the forces on individual
|
|
|
|
|
atoms are changed by the fix. The scalar vector values calculated by
|
|
|
|
|
this fix are "extensive", meaning they scale with the number of atoms
|
|
|
|
|
in the simulation.
|
2008-03-18 04:49:34 +08:00
|
|
|
</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.
|
2007-06-26 08:03:39 +08:00
|
|
|
</P>
|
|
|
|
|
<P>The forces due to this fix are imposed during an energy minimization,
|
|
|
|
|
invoked by the <A HREF = "minimize.html">minimize</A> command.
|
2006-09-22 00:22:34 +08:00
|
|
|
</P>
|
2008-08-01 23:10:00 +08:00
|
|
|
<P>IMPORTANT NOTE: If you want the fictitious potential energy associated
|
|
|
|
|
with the added forces 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>
|
2006-09-22 00:22:34 +08:00
|
|
|
<P><B>Restrictions:</B> none
|
|
|
|
|
</P>
|
|
|
|
|
<P><B>Related commands:</B>
|
|
|
|
|
</P>
|
|
|
|
|
<P><A HREF = "fix_setforce.html">fix setforce</A>, <A HREF = "fix_aveforce.html">fix aveforce</A>
|
|
|
|
|
</P>
|
|
|
|
|
<P><B>Default:</B> none
|
|
|
|
|
</P>
|
|
|
|
|
</HTML>
|
