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fix_append_atoms.html
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Wed, Jul 31, 01:35
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rLAMMPS lammps
fix_append_atoms.html
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<HTML>
<CENTER><A
HREF =
"http://lammps.sandia.gov"
>
LAMMPS WWW Site
</A>
-
<A
HREF =
"Manual.html"
>
LAMMPS Documentation
</A>
-
<A
HREF =
"Section_commands.html#comm"
>
LAMMPS Commands
</A>
</CENTER>
<HR>
<H3>
fix append/atoms command
</H3>
<P><B>
Syntax:
</B>
</P>
<PRE>
fix ID group-ID append/atoms face ... keyword value ...
</PRE>
<UL><LI>
ID, group-ID are documented in
<A
HREF =
"fix.html"
>
fix
</A>
command
<LI>
append/atoms = style name of this fix command
<LI>
face =
<I>
zhi
</I>
<LI>
zero or more keyword/value pairs may be appended
<LI>
keyword =
<I>
size
</I>
or
<I>
freq
</I>
or
<I>
temp
</I>
or
<I>
random
</I>
or
<I>
units
</I>
<PRE>
<I>
size
</I>
args = Lz
Lz = z size of lattice region appended in a single event(distance units)
<I>
freq
</I>
args = freq
freq = the number of timesteps between append events
<I>
temp
</I>
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)
<I>
random
</I>
args = xmax ymax zmax seed
<I>
xmax
</I>
,
<I>
ymax
</I>
,
<I>
zmax
</I>
= maximum displacement in particular direction (distance units)
<I>
seed
</I>
= random number seed for random displacement
<I>
units
</I>
value =
<I>
lattice
</I>
or
<I>
box
</I>
<I>
lattice
</I>
= the wall position is defined in lattice units
<I>
box
</I>
= the wall position is defined in simulation box units
</PRE>
</UL>
<P><B>
Examples:
</B>
</P>
<PRE>
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>
<P><B>
Description:
</B>
</P>
<P>
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
<A
HREF =
"create_box.html"
>
create_box
</A>
command.
Before using this command, a lattice must also be defined using the
<A
HREF =
"lattice.html"
>
lattice
</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
<I>
size
</I>
keyword defines the size in z of the chunk of material to
be added.
</P>
<P>
The
<I>
random
</I>
keyword will give the atoms random displacements around
their lattice points to simulate some initial temperature.
</P>
<P>
The
<I>
temp
</I>
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
<I>
extent
</I>
argument.
</P>
<P>
The
<I>
units
</I>
keyword determines the meaning of the distance units used
to define a wall position, but only when a numeric constant is used.
A
<I>
box
</I>
value selects standard distance units as defined by the
<A
HREF =
"units.html"
>
units
</A>
command, e.g. Angstroms for units = real or metal.
A
<I>
lattice
</I>
value means the distance units are in lattice spacings.
The
<A
HREF =
"lattice.html"
>
lattice
</A>
command must have been previously used to
define the lattice spacings.
</P>
<HR>
<P><B>
Restart, fix_modify, output, run start/stop, minimize info:
</B>
</P>
<P>
No information about this fix is written to
<A
HREF =
"restart.html"
>
binary restart
files
</A>
. None of the
<A
HREF =
"fix_modify.html"
>
fix_modify
</A>
options
are relevant to this fix. No global or per-atom quantities are stored
by this fix for access by various
<A
HREF =
"Section_howto.html#howto_15"
>
output
commands
</A>
. No parameter of this fix can
be used with the
<I>
start/stop
</I>
keywords of the
<A
HREF =
"run.html"
>
run
</A>
command.
This fix is not invoked during
<A
HREF =
"minimize.html"
>
energy minimization
</A>
.
</P>
<P><B>
Restrictions:
</B>
</P>
<P>
This fix style is part of the SHOCK package. It is only enabled if
LAMMPS was built with that package. See the
<A
HREF =
"Section_start.html#start_3"
>
Making
LAMMPS
</A>
section for more info.
</P>
<P>
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.
</P>
<P><B>
Related commands:
</B>
</P>
<P><A
HREF =
"fix_wall_piston.html"
>
fix wall/piston
</A>
command
</P>
<P><B>
Default:
</B>
</P>
<P>
The keyword defaults are size = 0.0, freq = 0, units = lattice.
</P>
</HTML>
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