git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@14950 f3b2605a-c512-4ea7-a41b-209d697bcdaa

doc/html/_sources/fix_addtorque.txt

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+.. index:: fix addtorque
+
+fix addtorque command
+=====================
+
+Syntax
+""""""
+
+.. parsed-literal::
+
+   fix ID group-ID addtorque Tx Ty Tz
+
+* ID, group-ID are documented in :doc:`fix <fix>` command
+* addtorque = style name of this fix command
+* Tx,Ty,Tz = torque component values (torque units)
+* any of Tx,Ty,Tz can be a variable (see below)
+
+
+Examples
+""""""""
+
+.. parsed-literal::
+
+   fix kick bead addtorque 2.0 3.0 5.0
+   fix kick bead addtorque 0.0 0.0 v_oscillate
+
+Description
+"""""""""""
+
+Add a set of forces to each atom in
+the group such that:
+
+* the components of the total torque applied on the group (around its
+  center of mass) are Tx,Ty,Tz
+* the group would move as a rigid body in the absence of other
+  forces.
+This command can be used to drive a group of atoms into rotation.
+
+Any of the 3 quantities defining the torque components can be specified
+as an equal-style :doc:`variable <variable>`, namely *Tx*\ ,
+*Ty*\ , *Tz*\ .  If the value is a variable, it should be specified as
+v_name, where name is the variable name.  In this case, the variable
+will be evaluated each timestep, and its value used to determine the
+torque component.
+
+Equal-style variables can specify formulas with various mathematical
+functions, and include :doc:`thermo_style <thermo_style>` command
+keywords for the simulation box parameters and timestep and elapsed
+time.  Thus it is easy to specify a time-dependent torque.
+
+
+----------
+
+
+Restart, fix_modify, output, run start/stop, minimize info
+""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
+
+No information about this fix is written to :doc:`binary restart files <restart>`.
+
+The :doc:`fix_modify <fix_modify>` *energy* option is supported by this
+fix to add the potential "energy" inferred by the added forces to the
+system's potential energy as part of :doc:`thermodynamic output <thermo_style>`.  This is a fictitious quantity but is
+needed so that the :doc:`minimize <minimize>` 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 forces.
+
+This fix computes a global scalar and a global 3-vector, which can be
+accessed by various :ref:`output commands <howto_15>`.
+The scalar is the potential energy discussed above.  The vector is the
+total torque on the group of atoms before the forces on individual
+atoms are changed by the fix.  The scalar and vector values calculated
+by this fix are "extensive".
+
+No parameter of this fix can be used with the *start/stop* keywords of
+the :doc:`run <run>` command.
+
+The forces due to this fix are imposed during an energy minimization,
+invoked by the :doc:`minimize <minimize>` command.  You should not
+specify force components with a variable that has time-dependence for
+use with a minimizer, since the minimizer increments the timestep as
+the iteration count during the minimization.
+
+Restrictions
+""""""""""""
+
+
+This fix is part of the USER-MISC package.  It is only enabled if
+LAMMPS was built with that package.  See the :ref:`Making LAMMPS <start_3>` section for more info.
+
+Related commands
+""""""""""""""""
+
+:doc:`fix addforce <fix_addforce>`
+
+**Default:** none
+
+
+.. _lws: http://lammps.sandia.gov
+.. _ld: Manual.html
+.. _lc: Section_commands.html#comm