2006-09-22 00:22:34 +08:00
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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 addforce command
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</H3>
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<P><B>Syntax:</B>
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</P>
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2009-08-09 06:03:37 +08:00
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<PRE>fix ID group-ID addforce fx fy fz keyword value ...
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2006-09-22 00:22:34 +08:00
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</PRE>
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2009-08-09 06:03:37 +08:00
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<UL><LI>ID, group-ID are documented in <A HREF = "fix.html">fix</A> command
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<LI>addforce = style name of this fix command
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2006-09-22 00:22:34 +08:00
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<LI>fx,fy,fz = force component values (force units)
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2009-08-09 06:03:37 +08:00
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<LI>zero or more keyword/value pairs may be appended to args
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<LI>keyword = <I>region</I>
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<PRE> <I>region</I> value = region-ID
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region-ID = ID of region atoms must be in to have added force
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</PRE>
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2006-09-22 00:22:34 +08:00
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</UL>
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<P><B>Examples:</B>
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</P>
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<PRE>fix kick flow addforce 1.0 0.0 0.0
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>Add fx,fy,fz to the corresponding component of force for each atom in
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the group. This command can be used to give an additional push to
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atoms in a simulation, such as for a simulation of Poiseuille flow in
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a channel.
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</P>
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2009-08-09 06:03:37 +08:00
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<P>If the <I>region</I> keyword is used, the atom must also be in the
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specified geometric <A HREF = "region.html">region</A> in order to have force added
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to it.
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</P>
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2007-10-11 06:28:11 +08:00
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<P><B>Restart, fix_modify, output, run start/stop, minimize info:</B>
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2007-06-26 08:03:39 +08:00
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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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2008-08-01 23:10:00 +08:00
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files</A>.
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2008-03-18 04:49:34 +08:00
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</P>
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2008-08-01 23:10:00 +08:00
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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 potential "energy" inferred by the added force 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>. This is a fictitious quantity but is
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needed so that the <A HREF = "minimize.html">minimize</A> command can include the
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forces added by this fix in a consistent manner. I.e. there is a
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decrease in potential energy when atoms move in the direction of the
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added force.
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</P>
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<P>This fix computes a scalar and a 3-vector of forces, which can be
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accessed by various <A HREF = "Section_howto.html#4_15">output commands</A>. The
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scalar is the potential energy discussed above. The vector is the
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total force on the group of atoms before the forces on individual
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atoms are changed by the fix. The scalar vector values calculated by
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2010-03-03 05:59:33 +08:00
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this fix are "extensive".
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2008-03-18 04:49:34 +08:00
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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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2007-06-26 08:03:39 +08:00
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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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2006-09-22 00:22:34 +08:00
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</P>
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2008-08-01 23:10:00 +08:00
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<P>IMPORTANT NOTE: If you want the fictitious potential energy associated
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with the added forces to be included in the total potential energy of
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the system (the quantity being minimized), you MUST enable the
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<A HREF = "fix_modify.html">fix_modify</A> <I>energy</I> option for this fix.
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</P>
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2006-09-22 00:22:34 +08:00
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<P><B>Restrictions:</B> none
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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_setforce.html">fix setforce</A>, <A HREF = "fix_aveforce.html">fix aveforce</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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