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@ -6,6 +6,9 @@ fix momentum command
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fix momentum/kk command
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=======================
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fix momentum/chunk command
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==========================
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Syntax
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""""""
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@ -16,6 +19,16 @@ Syntax
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* ID, group-ID are documented in :doc:`fix <fix>` command
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* momentum = style name of this fix command
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* N = adjust the momentum every this many timesteps
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one or more keyword/value pairs may be appended
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* keyword = *linear* or *angular* or *rescale*
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fix ID group-ID momentum/chunk N chunkID keyword values ...
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* ID, group-ID are documented in :doc:`fix <fix>` command
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* momentum/chunk = style name of this fix command
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* N = adjust the momentum per chunk every this many timesteps
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* chunkID = ID of :doc:`compute chunk/atom <compute_chunk_atom>` command
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one or more keyword/value pairs may be appended
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* keyword = *linear* or *angular* or *rescale*
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@ -24,9 +37,6 @@ Syntax
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*linear* values = xflag yflag zflag
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xflag,yflag,zflag = 0/1 to exclude/include each dimension
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*angular* values = none
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.. parsed-literal::
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*rescale* values = none
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Examples
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@ -37,19 +47,22 @@ Examples
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fix 1 all momentum 1 linear 1 1 0
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fix 1 all momentum 1 linear 1 1 1 rescale
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fix 1 all momentum 100 linear 1 1 1 angular
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fix 1 all momentum/chunk 100 molchunk linear 1 1 1 angular
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Description
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"""""""""""
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Zero the linear and/or angular momentum of the group of atoms every N
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timesteps by adjusting the velocities of the atoms. One (or both) of
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the *linear* or *angular* keywords must be specified.
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Fix momentum zeroes the linear and/or angular momentum of the group of
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atoms every N timesteps by adjusting the velocities of the atoms.
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Fix momentum/chunk works equivalently, but operates on a per-chunk basis.
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One (or both) of the *linear* or *angular* keywords **must** be specified.
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If the *linear* keyword is used, the linear momentum is zeroed by
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subtracting the center-of-mass velocity of the group from each atom.
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This does not change the relative velocity of any pair of atoms. One
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or more dimensions can be excluded from this operation by setting the
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corresponding flag to 0.
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subtracting the center-of-mass velocity of the group or chunk from each
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atom. This does not change the relative velocity of any pair of atoms.
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One or more dimensions can be excluded from this operation by setting
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the corresponding flag to 0.
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If the *angular* keyword is used, the angular momentum is zeroed by
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subtracting a rotational component from each atom.
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@ -60,7 +73,7 @@ to random perturbations (e.g. :doc:`fix langevin <fix_langevin>`
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thermostatting).
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The *rescale* keyword enables conserving the kinetic energy of the group
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of atoms by rescaling the velocities after the momentum was removed.
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or chunk of atoms by rescaling the velocities after the momentum was removed.
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Note that the :doc:`velocity <velocity>` command can be used to create
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initial velocities with zero aggregate linear and/or angular momentum.
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@ -71,15 +84,21 @@ initial velocities with zero aggregate linear and/or angular momentum.
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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 :doc:`binary restart files <restart>`. None of the :doc:`fix_modify <fix_modify>` options
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are relevant to this fix. No global or per-atom quantities are stored
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by this fix for access by various :doc:`output commands <Howto_output>`.
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No information about this fix is written to :doc:`binary restart files
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<restart>`. None of the :doc:`fix_modify <fix_modify>` options are
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relevant to this fix. No global or per-atom quantities are stored by
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this fix for access by various :doc:`output commands <Howto_output>`.
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No parameter of this fix can be used with the *start/stop* keywords of
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the :doc:`run <run>` command. This fix is not invoked during :doc:`energy minimization <minimize>`.
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the :doc:`run <run>` command. This fix is not invoked during
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:doc:`energy minimization <minimize>`.
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Restrictions
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""""""""""""
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none
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Fix momentum/chunk is part of the USER-MISC package. It is only enabled
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if LAMMPS was built with that package. See the :doc:`Build package
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<Build_package>` doc page for more info.
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Related commands
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""""""""""""""""
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Axel Kohlmeyer