forked from lijiext/lammps
94 lines
3.1 KiB
Plaintext
94 lines
3.1 KiB
Plaintext
"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
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:link(lws,http://lammps.sandia.gov)
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:link(ld,Manual.html)
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:link(lc,Section_commands.html#comm)
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:line
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fix addtorque command :h3
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[Syntax:]
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fix ID group-ID addtorque Tx Ty Tz :pre
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ID, group-ID are documented in "fix"_fix.html command :ulb,l
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addtorque = style name of this fix command :l
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Tx,Ty,Tz = torque component values (torque units) :l
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any of Tx,Ty,Tz can be a variable (see below) :l
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:ule
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[Examples:]
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fix kick bead addtorque 2.0 3.0 5.0
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fix kick bead addtorque 0.0 0.0 v_oscillate :pre
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[Description:]
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Add a set of forces to each atom in
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the group such that:
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the components of the total torque applied on the group (around its
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center of mass) are Tx,Ty,Tz :ulb,l
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the group would move as a rigid body in the absence of other
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forces. :l,ule
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This command can be used to drive a group of atoms into rotation.
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Any of the 3 quantities defining the torque components can be specified
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as an equal-style "variable"_variable.html, namely {Tx},
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{Ty}, {Tz}. 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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Equal-style variables can specify formulas with various mathematical
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functions, and include "thermo_style"_thermo_style.html 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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:line
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[Restart, fix_modify, output, run start/stop, minimize info:]
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No information about this fix is written to "binary restart
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files"_restart.html.
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The "fix_modify"_fix_modify.html {energy} 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 "thermodynamic
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output"_thermo_style.html. This is a fictitious quantity but is
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needed so that the "minimize"_minimize.html 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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This fix computes a global scalar and a global 3-vector, which can be
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accessed by various "output commands"_Section_howto.html#howto_15.
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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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No parameter of this fix can be used with the {start/stop} keywords of
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the "run"_run.html command.
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The forces due to this fix are imposed during an energy minimization,
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invoked by the "minimize"_minimize.html 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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[Restrictions:]
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This fix is part of the USER-MISC package. It is only enabled if
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LAMMPS was built with that package. See the "Making
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LAMMPS"_Section_start.html#start_3 section for more info.
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[Related commands:]
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"fix addforce"_fix_addforce.html
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[Default:] none
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