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< title > fix append/atoms command — LAMMPS documentation< / title >
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< li > fix append/atoms command< / li >
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< span id = "index-0" > < / span > < h1 > fix append/atoms command< a class = "headerlink" href = "#fix-append-atoms-command" title = "Permalink to this headline" > ¶< / a > < / h1 >
< div class = "section" id = "syntax" >
< h2 > Syntax< a class = "headerlink" href = "#syntax" title = "Permalink to this headline" > ¶< / a > < / h2 >
< div class = "highlight-python" > < div class = "highlight" > < pre > fix ID group-ID append/atoms face ... keyword value ...
< / pre > < / div >
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< ul class = "simple" >
< li > ID, group-ID are documented in < a class = "reference internal" href = "fix.html" > < em > fix< / em > < / a > command< / li >
< li > append/atoms = style name of this fix command< / li >
< li > face = < em > zhi< / em > < / li >
< li > zero or more keyword/value pairs may be appended< / li >
< li > keyword = < em > basis< / em > or < em > size< / em > or < em > freq< / em > or < em > temp< / em > or < em > random< / em > or < em > units< / em > < / li >
< / ul >
< pre class = "literal-block" >
< em > basis< / em > values = M itype
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M = which basis atom
itype = atom type (1-N) to assign to this basis atom
< em > size< / em > args = Lz
Lz = z size of lattice region appended in a single event(distance units)
< em > freq< / em > args = freq
freq = the number of timesteps between append events
< em > temp< / em > 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)
< em > random< / em > args = xmax ymax zmax seed
< em > xmax< / em > , < em > ymax< / em > , < em > zmax< / em > = maximum displacement in particular direction (distance units)
< em > seed< / em > = random number seed for random displacement
< em > units< / em > value = < em > lattice< / em > or < em > box< / em >
< em > lattice< / em > = the wall position is defined in lattice units
< em > box< / em > = the wall position is defined in simulation box units
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< / pre >
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< div class = "section" id = "examples" >
< h2 > Examples< a class = "headerlink" href = "#examples" title = "Permalink to this headline" > ¶< / a > < / h2 >
< div class = "highlight-python" > < div class = "highlight" > < pre > 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
< / pre > < / div >
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< div class = "section" id = "description" >
< h2 > Description< a class = "headerlink" href = "#description" title = "Permalink to this headline" > ¶< / a > < / h2 >
< p > 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
from zlo. This allows the system to grow with time to accommodate an
expanding wave. A simulation box must already exist, which is
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typically created via the < a class = "reference internal" href = "create_box.html" > < em > create_box< / em > < / a > command.
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Before using this command, a lattice must also be defined using the
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< a class = "reference internal" href = "lattice.html" > < em > lattice< / em > < / a > command.< / p >
< p > This fix will automatically freeze atoms on the zhi edge of the
system, so that overlaps are avoided when new atoms are appended.< / p >
< p > The < em > basis< / em > 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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< a class = "reference internal" href = "lattice.html" > < em > lattice< / em > < / a > 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.< / p >
< p > The < em > size< / em > keyword defines the size in z of the chunk of material to
be added.< / p >
< p > The < em > random< / em > keyword will give the atoms random displacements around
their lattice points to simulate some initial temperature.< / p >
< p > The < em > temp< / em > 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 < em > extent< / em > argument.< / p >
< p > The < em > units< / em > 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 < em > box< / em > value selects standard distance units as defined by the
< a class = "reference internal" href = "units.html" > < em > units< / em > < / a > command, e.g. Angstroms for units = real or metal.
A < em > lattice< / em > value means the distance units are in lattice spacings.
The < a class = "reference internal" href = "lattice.html" > < em > lattice< / em > < / a > command must have been previously used to
define the lattice spacings.< / p >
< / div >
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< div class = "section" id = "restart-fix-modify-output-run-start-stop-minimize-info" >
< h2 > Restart, fix_modify, output, run start/stop, minimize info< a class = "headerlink" href = "#restart-fix-modify-output-run-start-stop-minimize-info" title = "Permalink to this headline" > ¶< / a > < / h2 >
< p > No information about this fix is written to < a class = "reference internal" href = "restart.html" > < em > binary restart files< / em > < / a > . None of the < a class = "reference internal" href = "fix_modify.html" > < em > fix_modify< / em > < / a > 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 < a class = "reference internal" href = "Section_howto.html#howto-15" > < span > output commands< / span > < / a > . No parameter of this fix can
be used with the < em > start/stop< / em > keywords of the < a class = "reference internal" href = "run.html" > < em > run< / em > < / a > command.
This fix is not invoked during < a class = "reference internal" href = "minimize.html" > < em > energy minimization< / em > < / a > .< / p >
< / div >
< div class = "section" id = "restrictions" >
< h2 > Restrictions< a class = "headerlink" href = "#restrictions" title = "Permalink to this headline" > ¶< / a > < / h2 >
< p > This fix style is part of the SHOCK package. It is only enabled if
LAMMPS was built with that package. See the < a class = "reference internal" href = "Section_start.html#start-3" > < span > Making LAMMPS< / span > < / a > section for more info.< / p >
< p > 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.< / p >
< / div >
< div class = "section" id = "related-commands" >
< h2 > Related commands< a class = "headerlink" href = "#related-commands" title = "Permalink to this headline" > ¶< / a > < / h2 >
< p > < a class = "reference internal" href = "fix_wall_piston.html" > < em > fix wall/piston< / em > < / a > command< / p >
< / div >
< div class = "section" id = "default" >
< h2 > Default< a class = "headerlink" href = "#default" title = "Permalink to this headline" > ¶< / a > < / h2 >
< p > The keyword defaults are size = 0.0, freq = 0, units = lattice. All
added atoms are of type 1 unless the basis keyword is used.< / p >
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