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fix_append_atoms.txt
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.. index:: fix append/atoms
fix append/atoms command
========================
Syntax
""""""
.. parsed-literal::
fix ID group-ID append/atoms face ... keyword value ...
* ID, group-ID are documented in :doc:`fix <fix>` command
* append/atoms = style name of this fix command
* face = *zhi*
* zero or more keyword/value pairs may be appended
* keyword = *basis* or *size* or *freq* or *temp* or *random* or *units*
.. parsed-literal::
*basis* values = M itype
M = which basis atom
itype = atom type (1-N) to assign to this basis atom
*size* args = Lz
Lz = z size of lattice region appended in a single event(distance units)
*freq* args = freq
freq = the number of timesteps between append events
*temp* args = target damp seed extent
target = target temperature for the region between zhi-extent and zhi (temperature units)
damp = damping parameter (time units)
seed = random number seed for langevin kicks
extent = extent of thermostated region (distance units)
*random* args = xmax ymax zmax seed
*xmax*, *ymax*, *zmax* = maximum displacement in particular direction (distance units)
*seed* = random number seed for random displacement
*units* value = *lattice* or *box*
*lattice* = the wall position is defined in lattice units
*box* = the wall position is defined in simulation box units
Examples
""""""""
.. parsed-literal::
fix 1 all append/atoms zhi size 5.0 freq 295 units lattice
fix 4 all append/atoms zhi size 15.0 freq 5 units box
fix A all append/atoms zhi size 1.0 freq 1000 units lattice
Description
"""""""""""
This fix creates atoms on a lattice, appended on the zhi edge of the
system box. This can be useful when a shock or wave is propagating
from zlo. This allows the system to grow with time to accommodate an
expanding wave. A simulation box must already exist, which is
typically created via the :doc:`create_box <create_box>` command.
Before using this command, a lattice must also be defined using the
:doc:`lattice <lattice>` command.
This fix will automatically freeze atoms on the zhi edge of the
system, so that overlaps are avoided when new atoms are appended.
The *basis* keyword specifies an atom type that will be assigned to
specific basis atoms as they are created. See the
:doc:`lattice <lattice>` command for specifics on how basis atoms are
defined for the unit cell of the lattice. By default, all created
atoms are assigned type = 1 unless this keyword specifies differently.
The *size* keyword defines the size in z of the chunk of material to
be added.
The *random* keyword will give the atoms random displacements around
their lattice points to simulate some initial temperature.
The *temp* keyword will cause a region to be thermostated with a
Langevin thermostat on the zhi boundary. The size of the region is
measured from zhi and is set with the *extent* argument.
The *units* keyword determines the meaning of the distance units used
to define a wall position, but only when a numeric constant is used.
A *box* value selects standard distance units as defined by the
:doc:`units <units>` command, e.g. Angstroms for units = real or metal.
A *lattice* value means the distance units are in lattice spacings.
The :doc:`lattice <lattice>` command must have been previously used to
define the lattice spacings.
----------
Restart, fix_modify, output, run start/stop, minimize info
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
No information about this fix is written to :doc:`binary restart files <restart>`. None of the :doc:`fix_modify <fix_modify>` options
are relevant to this fix. No global or per-atom quantities are stored
by this fix for access by various :ref:`output commands <howto_15>`. No parameter of this fix can
be used with the *start/stop* keywords of the :doc:`run <run>` command.
This fix is not invoked during :doc:`energy minimization <minimize>`.
Restrictions
""""""""""""
This fix style is part of the SHOCK package. It is only enabled if
LAMMPS was built with that package. See the :ref:`Making LAMMPS <start_3>` section for more info.
The boundary on which atoms are added with append/atoms must be
shrink/minimum. The opposite boundary may be any boundary type other
than periodic.
Related commands
""""""""""""""""
:doc:`fix wall/piston <fix_wall_piston>` command
Default
"""""""
The keyword defaults are size = 0.0, freq = 0, units = lattice. All
added atoms are of type 1 unless the basis keyword is used.
.. _lws: http://lammps.sandia.gov
.. _ld: Manual.html
.. _lc: Section_commands.html#comm
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