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 spring/self 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 spring/self K
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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>spring/self = style name of this fix command
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<LI>K = spring constant (force/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 tether boundary-atoms spring/self 10.0
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>Apply a spring force independently to each atom in the group to tether
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it to its initial position. The initial position for each atom is its
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location at the time the fix command was issued. At each timestep,
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the magnitude of the force on each atom is -Kr, where r is the
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displacement of the atom from its current position to its initial
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position.
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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>This fix writes the original coordinates of tethered atoms to <A HREF = "restart.html">binary
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restart files</A>, so that the spring effect will be the
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same in a restarted simulation. See the
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<A HREF = "read_restart.html">read_restart</A> command for info on how to re-specify
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a fix in an input script that reads a restart file, so that the
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operation of the fix continues in an uninterrupted fashion.
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</P>
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2008-06-07 07:21:53 +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 energy stored in the per-atom springs to the system's
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potential energy as part of <A HREF = "thermo_style.html">thermodynamic output</A>.
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</P>
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2010-04-03 00:51:06 +08:00
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<P>This fix computes a global scalar which can be accessed by various
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2011-08-26 01:01:01 +08:00
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<A HREF = "Section_howto.html#howto_15">output commands</A>. The scalar is an
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energy which is the sum of the spring energy for each atom, where the
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2010-04-03 00:51:06 +08:00
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per-atom energy is 0.5 * K * r^2. The scalar value calculated by this
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fix is "extensive".
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2008-06-07 07:21:53 +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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</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 per-atom spring energy to be included
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in the total potential energy of the system (the quantity being
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minimized), you MUST enable the <A HREF = "fix_modify.html">fix_modify</A> <I>energy</I>
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option for this fix.
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2007-06-26 08:03:39 +08:00
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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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2008-05-16 06:05:51 +08:00
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<P><A HREF = "fix_drag.html">fix drag</A>, <A HREF = "fix_spring.html">fix spring</A>,
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<A HREF = "fix_smd.html">fix smd</A>, <A HREF = "fix_spring_rg.html">fix spring/rg</A>
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2006-09-22 00:22:34 +08:00
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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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