forked from lijiext/lammps
127 lines
4.5 KiB
Plaintext
127 lines
4.5 KiB
Plaintext
.. 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
|