2011-08-09 05:22:57 +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 addtorque 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 addtorque Tx Ty Tz
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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>addtorque = style name of this fix command
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<LI>Tx,Ty,Tz = torque component values (torque units)
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<LI>any of Tx,Ty,Tz can be a variable (see below)
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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 bead addtorque 2.0 3.0 5.0
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fix kick bead addtorque 0.0 0.0 v_oscillate
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</PRE>
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<P><B>Description:</B>
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</P>
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2011-08-09 07:55:30 +08:00
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<P>Add a set of forces to each atom in
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2011-08-09 05:22:57 +08:00
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the group such that:
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2011-08-09 07:55:30 +08:00
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</P>
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<UL><LI>the components of the total torque applied on the group (around its
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center of mass) are Tx,Ty,Tz
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2011-08-09 05:22:57 +08:00
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2011-08-09 07:55:30 +08:00
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<LI>the group would move as a rigid body in the absence of other
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forces.
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2011-08-09 05:22:57 +08:00
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</UL>
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<P>This command can be used to drive a group of atoms into rotation.
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</P>
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<P>Any of the 3 quantities defining the torque components can be specified
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as an equal-style <A HREF = "variable.html">variable</A>, namely <I>Tx</I>,
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<I>Ty</I>, <I>Tz</I>. If the value is a variable, it should be specified as
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v_name, where name is the variable name. In this case, the variable
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will be evaluated each timestep, and its value used to determine the
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torque component.
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</P>
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<P>Equal-style variables can specify formulas with various mathematical
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functions, and include <A HREF = "thermo_style.html">thermo_style</A> command
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keywords for the simulation box parameters and timestep and elapsed
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time. Thus it is easy to specify a time-dependent torque.
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</P>
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<HR>
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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 potential "energy" inferred by the added forces 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 forces.
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</P>
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2011-08-26 01:01:01 +08:00
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<P>This fix computes a global scalar and a global 3-vector, which can be
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accessed by various <A HREF = "Section_howto.html#howto_15">output commands</A>.
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The scalar is the potential energy discussed above. The vector is the
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total torque on the group of atoms before the forces on individual
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atoms are changed by the fix. The scalar and vector values calculated
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by this fix are "extensive".
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2011-08-09 05:22:57 +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. You should not
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specify force components with a variable that has time-dependence for
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use with a minimizer, since the minimizer increments the timestep as
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the iteration count during the minimization.
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</P>
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<P><B>Restrictions:</B>
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</P>
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2011-08-27 02:53:00 +08:00
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<P>This fix is part of the USER-MISC package. It is only enabled if
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2011-08-26 00:46:23 +08:00
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LAMMPS was built with that package. See the <A HREF = "Section_start.html#start_3">Making
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2011-08-09 05:22:57 +08:00
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LAMMPS</A> section for more info.
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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_addforce.html">fix addforce</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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