forked from lijiext/lammps
134 lines
5.6 KiB
HTML
134 lines
5.6 KiB
HTML
<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>create_atoms command
|
|
</H3>
|
|
<P><B>Syntax:</B>
|
|
</P>
|
|
<PRE>create_atoms type style args keyword values ...
|
|
</PRE>
|
|
<UL><LI>type = atom type (1-Ntypes) of atoms to create
|
|
|
|
<LI>style = <I>box</I> or <I>region</I> or <I>single</I>
|
|
|
|
<PRE> <I>box</I> args = none
|
|
<I>region</I> args = region-ID
|
|
region-ID = atoms will only be created if contained in the region
|
|
<I>single</I> args = x y z
|
|
x,y,z = coordinates of a single atom (distance units)
|
|
</PRE>
|
|
<LI>zero or more keyword/value pairs may be appended
|
|
|
|
<LI>keyword = <I>basis</I> or <I>units</I>
|
|
|
|
<PRE> <I>basis</I> values = M itype
|
|
M = which basis atom
|
|
itype = atom type (1-N) to assign to this basis atom
|
|
<I>units</I> value = <I>lattice</I> or <I>box</I>
|
|
<I>lattice</I> = the geometry is defined in lattice units
|
|
<I>box</I> = the geometry is defined in simulation box units
|
|
</PRE>
|
|
|
|
</UL>
|
|
<P><B>Examples:</B>
|
|
</P>
|
|
<PRE>create_atoms 1 box
|
|
create_atoms 3 region regsphere basis 2 3
|
|
create_atoms 3 single 0 0 5
|
|
</PRE>
|
|
<P><B>Description:</B>
|
|
</P>
|
|
<P>This command creates atoms on a lattice or a single atom as an
|
|
alternative to reading in their coordinates via a
|
|
<A HREF = "read_data.html">read_data</A> or <A HREF = "read_restart.html">read_restart</A>
|
|
command. 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. The only exception is for the
|
|
<I>single</I> style with units = box.
|
|
</P>
|
|
<P>For the <I>box</I> style, the create_atoms command fills the entire
|
|
simulation box with atoms on the lattice. If your simulation box is
|
|
periodic, you should insure its size is a multiple of the lattice
|
|
spacings, to avoid unwanted atom overlaps at the box boundaries. If
|
|
your box is periodic and a multiple of the lattice spacing in a
|
|
particular dimension, LAMMPS is careful to put exactly one atom at the
|
|
boundary (on either side of the box), not zero or two.
|
|
</P>
|
|
<P>For the <I>region</I> style, the geometric volume is filled that is inside
|
|
the simulation box and is also consistent with the region volume. See
|
|
the <A HREF = "region.html">region</A> command for details. Note that a region can
|
|
be specified so that its "volume" is either inside or outside a
|
|
geometric boundary. Also note that if your region is the same size as
|
|
a periodic simulation box (in some dimension), LAMMPS does not
|
|
implement the same logic as with the <I>box</I> style, to insure exactly
|
|
one atom at the boundary. if this is what you desire, you should
|
|
either use the <I>box</I> style, or tweak the region size to get precisely
|
|
the atoms you want.
|
|
</P>
|
|
<P>For the <I>single</I> style, a single atom is added to the system at the
|
|
specified coordinates. This can be useful for debugging purposes or
|
|
to create a tiny system with a handful of atoms at specified
|
|
positions.
|
|
</P>
|
|
<P>The <I>basis</I> keyword specifies an atom type that will be assigned to
|
|
specific basis atoms as they are created. See the
|
|
<A HREF = "lattice.html">lattice</A> command for specifics on how basis atoms are
|
|
defined for the unit cell of the lattice. By default, all created
|
|
atoms are assigned the argument <I>type</I> as their atom type.
|
|
</P>
|
|
<P>The <I>units</I> keyword determines the meaning of the distance units used
|
|
to specify the coordinates of the one atom created by the <I>single</I>
|
|
style. 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.
|
|
</P>
|
|
<P>Note that this command adds atoms to those that already exist. By
|
|
using the create_atoms command multiple times, multiple sets of atoms
|
|
can be added to the simulation. For example, interleaving
|
|
create_atoms with <A HREF = "lattice.html">lattice</A> commands specifying different
|
|
orientations, grain boundaries can be created. By using the
|
|
create_atoms command in conjunction with the
|
|
<A HREF = "delete_atoms.html">delete_atoms</A> command, reasonably complex
|
|
geometries can be created. The create_atoms command can also be used
|
|
to add atoms to a system previously read in from a data or restart
|
|
file. In all these cases, care should be taken to insure that new
|
|
atoms do not overlap existing atoms inappropriately. The
|
|
<A HREF = "delete_atoms.html">delete_atoms</A> command can be used to handle
|
|
overlaps.
|
|
</P>
|
|
<P>Aside from their position and atom type, other properties of created
|
|
atoms are set to 0.0, e.g velocity, charge, etc. These properties can
|
|
be changed via the <A HREF = "velocity.html">velocity</A> or <A HREF = "set.html">set</A>
|
|
commands.
|
|
</P>
|
|
<P>Atom IDs are assigned to created atoms in the following way. The
|
|
collection of created atoms are assigned consecutive IDs that start
|
|
immediately following the largest atom ID existing before the
|
|
create_atoms command was invoked. When a simulation is performed on
|
|
different numbers of processors, there is no guarantee a particular
|
|
created atom will be assigned the same ID.
|
|
</P>
|
|
<P><B>Restrictions:</B>
|
|
</P>
|
|
<P>An <A HREF = "atom_style.html">atom_style</A> must be previously defined to use this
|
|
command.
|
|
</P>
|
|
<P><B>Related commands:</B>
|
|
</P>
|
|
<P><A HREF = "lattice.html">lattice</A>, <A HREF = "region.html">region</A>, <A HREF = "create_box.html">create_box</A>,
|
|
<A HREF = "read_data.html">read_data</A>, <A HREF = "read_restart.html">read_restart</A>
|
|
</P>
|
|
<P><B>Default:</B> none
|
|
</P>
|
|
</HTML>
|