"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c

:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Section_commands.html#comm)

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fix append/atoms command :h3

[Syntax:]

fix ID group-ID append/atoms face ... keyword value ... :pre

ID, group-ID are documented in "fix"_fix.html command :ulb,l
append/atoms = style name of this fix command :l
face = {zhi} :l
zero or more keyword/value pairs may be appended :l
keyword = {basis} or {size} or {freq} or {temp} or {random} or {units}  :l
  {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 velocity for region immediately ahead of the piston
    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 :pre
:ule

[Examples:]

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 :pre

[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 "create_box"_create_box.html command.
Before using this command, a lattice must also be defined using the
"lattice"_lattice.html 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
"lattice"_lattice.html 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
"units"_units.html command, e.g. Angstroms for units = real or metal.
A {lattice} value means the distance units are in lattice spacings.
The "lattice"_lattice.html command must have been previously used to
define the lattice spacings.

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[Restart, fix_modify, output, run start/stop, minimize info:]

No information about this fix is written to "binary restart
files"_restart.html.  None of the "fix_modify"_fix_modify.html options
are relevant to this fix.  No global or per-atom quantities are stored
by this fix for access by various "output
commands"_Section_howto.html#howto_15.  No parameter of this fix can
be used with the {start/stop} keywords of the "run"_run.html command.
This fix is not invoked during "energy minimization"_minimize.html.

[Restrictions:]

This fix style is part of the SHOCK package.  It is only enabled if
LAMMPS was built with that package. See the "Making
LAMMPS"_Section_start.html#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:]

"fix wall/piston"_fix_wall_piston.html 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.
