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Mon, Jul 28, 04:31
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rLAMMPS lammps
lattice.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>
lattice command
</H3>
<P><B>
Syntax:
</B>
</P>
<PRE>
lattice style value
</PRE>
<UL><LI>
style =
<I>
none
</I>
or
<I>
sc
</I>
or
<I>
bcc
</I>
or
<I>
fcc
</I>
or
<I>
sq
</I>
or
<I>
sq2
</I>
or
<I>
hex
</I>
or
<I>
diamond
</I>
<PRE>
<I>
none
</I>
value = none
for all other styles:
value = reduced density (for LJ units)
value = cubic lattice constant in Angstroms (for real or metal units)
</PRE>
</UL>
<P><B>
Examples:
</B>
</P>
<PRE>
lattice fcc 3.52
lattice hex 0.85
lattice none
</PRE>
<P><B>
Description:
</B>
</P>
<P>
Define a lattice type and lattice constant. This is required before
using a commands that (optionally) use the lattice, such as
<A
HREF =
"create_atoms.html"
>
create_atoms
</A>
or
<A
HREF =
"region.html"
>
region
</A>
. The lattice
type must be consistent with the dimension of the simulation - see the
<A
HREF =
"dimension.html"
>
dimension
</A>
command. Styles
<I>
sc
</I>
or
<I>
bcc
</I>
or
<I>
fcc
</I>
or
<I>
diamond
</I>
are for 3d problems. Styles
<I>
sq
</I>
or
<I>
sq2
</I>
or
<I>
hex
</I>
are for
2d problems. Lattices of style
<I>
fcc
</I>
,
<I>
bcc
</I>
,
<I>
hex
</I>
, or
<I>
diamond
</I>
are
described in any solid-state physics text. A
<I>
sc
</I>
lattice is simple
cubic, with atoms at the corners of a cube. A
<I>
sq
</I>
lattice is square
with atoms at the corners of a square. A
<I>
sq2
</I>
lattice is a
<I>
sq
</I>
lattice with an additional atom at the center of the square.
</P>
<P>
For unit style
<I>
real
</I>
or
<I>
metal
</I>
, the specified value is the cubic
lattice constant in Angstroms. For unit style
<I>
lj
</I>
, the value is the
reduced density (rho*) which LAMMPS converts into a cubic lattice
constant. For 3d problems, the relationship "rho* = rho sigma^3" is
used for the conversion, where rho = N/V with V = the volume of the
cubic cell and N = 4 for
<I>
fcc
</I>
, 2 for
<I>
bcc
</I>
, 1 for
<I>
sc
</I>
, and 8 for
<I>
diamond
</I>
lattices. For 2d problems, the relationship "rho* = rho
sigma^2" is used for the conversion, where N = 2 for
<I>
sq2
</I>
or
<I>
hex
</I>
and 1 for
<I>
sq
</I>
. In the hex case, the unit cell is actually
rectangular; it is extended by a factor of sqrt(3) in the y-dimension.
</P>
<P>
The command "lattice none" can be used to turn off the lattice
setting. Any command that attempts to use a lattice constant will
then generate an error.
</P>
<P><B>
Restrictions:
</B>
none
</P>
<P><B>
Related commands:
</B>
</P>
<P><A
HREF =
"dimension.html"
>
dimension
</A>
,
<A
HREF =
"orient.html"
>
orient
</A>
,
<A
HREF =
"origin.html"
>
origin
</A>
,
<A
HREF =
"create_atoms.html"
>
create_atoms
</A>
,
<A
HREF =
"region.html"
>
region
</A>
</P>
<P><B>
Default:
</B>
</P>
<PRE>
lattice none
</PRE>
</HTML>
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