forked from lijiext/lammps
127 lines
4.5 KiB
Plaintext
127 lines
4.5 KiB
Plaintext
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.. index:: fix append/atoms
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fix append/atoms command
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========================
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Syntax
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""""""
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.. parsed-literal::
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fix ID group-ID append/atoms face ... keyword value ...
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* ID, group-ID are documented in :doc:`fix <fix>` command
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* append/atoms = style name of this fix command
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* face = *zhi*
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* zero or more keyword/value pairs may be appended
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* keyword = *basis* or *size* or *freq* or *temp* or *random* or *units*
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.. parsed-literal::
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*basis* values = M itype
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M = which basis atom
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itype = atom type (1-N) to assign to this basis atom
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*size* args = Lz
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Lz = z size of lattice region appended in a single event(distance units)
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*freq* args = freq
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freq = the number of timesteps between append events
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*temp* args = target damp seed extent
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target = target temperature for the region between zhi-extent and zhi (temperature units)
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damp = damping parameter (time units)
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seed = random number seed for langevin kicks
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extent = extent of thermostated region (distance units)
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*random* args = xmax ymax zmax seed
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*xmax*\ , *ymax*\ , *zmax* = maximum displacement in particular direction (distance units)
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*seed* = random number seed for random displacement
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*units* value = *lattice* or *box*
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*lattice* = the wall position is defined in lattice units
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*box* = the wall position is defined in simulation box units
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Examples
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""""""""
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.. parsed-literal::
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fix 1 all append/atoms zhi size 5.0 freq 295 units lattice
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fix 4 all append/atoms zhi size 15.0 freq 5 units box
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fix A all append/atoms zhi size 1.0 freq 1000 units lattice
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Description
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"""""""""""
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This fix creates atoms on a lattice, appended on the zhi edge of the
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system box. This can be useful when a shock or wave is propagating
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from zlo. This allows the system to grow with time to accommodate an
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expanding wave. A simulation box must already exist, which is
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typically created via the :doc:`create_box <create_box>` command.
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Before using this command, a lattice must also be defined using the
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:doc:`lattice <lattice>` command.
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This fix will automatically freeze atoms on the zhi edge of the
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system, so that overlaps are avoided when new atoms are appended.
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The *basis* keyword specifies an atom type that will be assigned to
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specific basis atoms as they are created. See the
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:doc:`lattice <lattice>` command for specifics on how basis atoms are
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defined for the unit cell of the lattice. By default, all created
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atoms are assigned type = 1 unless this keyword specifies differently.
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The *size* keyword defines the size in z of the chunk of material to
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be added.
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The *random* keyword will give the atoms random displacements around
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their lattice points to simulate some initial temperature.
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The *temp* keyword will cause a region to be thermostated with a
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Langevin thermostat on the zhi boundary. The size of the region is
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measured from zhi and is set with the *extent* argument.
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The *units* keyword determines the meaning of the distance units used
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to define a wall position, but only when a numeric constant is used.
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A *box* value selects standard distance units as defined by the
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:doc:`units <units>` command, e.g. Angstroms for units = real or metal.
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A *lattice* value means the distance units are in lattice spacings.
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The :doc:`lattice <lattice>` command must have been previously used to
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define the lattice spacings.
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----------
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Restart, fix_modify, output, run start/stop, minimize info
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""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
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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 :ref:`output commands <howto_15>`. No parameter of this fix can
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be used with the *start/stop* keywords of the :doc:`run <run>` command.
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This fix is not invoked during :doc:`energy minimization <minimize>`.
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Restrictions
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""""""""""""
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This fix style is part of the SHOCK package. It is only enabled if
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LAMMPS was built with that package. See the :ref:`Making LAMMPS <start_3>` section for more info.
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The boundary on which atoms are added with append/atoms must be
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shrink/minimum. The opposite boundary may be any boundary type other
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than periodic.
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Related commands
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""""""""""""""""
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:doc:`fix wall/piston <fix_wall_piston>` command
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Default
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"""""""
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The keyword defaults are size = 0.0, freq = 0, units = lattice. All
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added atoms are of type 1 unless the basis keyword is used.
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.. _lws: http://lammps.sandia.gov
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.. _ld: Manual.html
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.. _lc: Section_commands.html#comm
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