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Mon, Oct 14, 12:22
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rLAMMPS lammps
shape.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>
shape command
</H3>
<P><B>
Syntax:
</B>
</P>
<PRE>
shape I x y z
</PRE>
<UL><LI>
I = atom type (see asterisk form below)
<LI>
x = x diameter (distance units)
<LI>
y = y diameter (distance units)
<LI>
z = z diameter (distance units)
</UL>
<P><B>
Examples:
</B>
</P>
<PRE>
shape 1 1.0 1.0 1.0
shape * 3.0 1.0 1.0
shape 2* 3.0 1.0 1.0
</PRE>
<P><B>
Description:
</B>
</P>
<P>
Set the shape for all atoms of one or more atom types. In LAMMPS,
particles that have a finite size are said to have a "shape", as
opposed to being a point mass. Shape values can also be set in the
<A
HREF =
"read_data.html"
>
read_data
</A>
data file using the "Shapes" keyword. See
the
<A
HREF =
"units.html"
>
units
</A>
command for what distance units to use.
</P>
<P>
The I index can be specified in one of two ways. An explicit numeric
value can be used, as in the 1st example above. Or a wild-card
asterisk can be used to set the shape for multiple atom types. This
takes the form "*" or "*n" or "n*" or "m*n". If N = the number of
atom types, then an asterisk with no numeric values means all types
from 1 to N. A leading asterisk means all types from 1 to n
(inclusive). A trailing asterisk means all types from n to N
(inclusive). A middle asterisk means all types from m to n
(inclusive).
</P>
<P>
A line in a
<A
HREF =
"read_data.html"
>
data file
</A>
that follows the "Shapes"
keyword specifies shape using the same format as the arguments of the
shape command in an input script, except that no wild-card asterisk
can be used. For example, under the "Shapes" section of a data file,
the line that corresponds to the 1st example above would be listed as
</P>
<PRE>
1 1.0 1.0 1.0
</PRE>
<P>
The shape values can be set to 0.0, which means that atoms of that
type are point masses and not finite-size particles. Pair styles and
fixes that rely on particles having a finite size should not be used
for such particles.
</P>
<P>
Note that the shape command can only be used if the
<A
HREF =
"atom_style.html"
>
atom
style
</A>
requires per-type atom shape to be set.
Currently, only the
<I>
dipole
</I>
and
<I>
ellipsoid
</I>
styles do. The
<I>
granular
</I>
and
<I>
peri
</I>
styles require the shape to be set for indivual
particles, not types. For these styles, the only option currently
allowed is for spherical particles, so a single diameter value
suffices to determine the shape. Per-atom diameters are defined in
the data file read by the
<A
HREF =
"read_data.html"
>
read_data
</A>
command, or set
to default values by the
<A
HREF =
"create_atoms.html"
>
create_atoms
</A>
command, or
set to new values by the
<A
HREF =
"set.html"
>
set diamter
</A>
command.
</P>
<P>
Dipoles use the atom shape to compute a moment of inertia for
rotational energy. See the
<A
HREF =
"pair_dipole.html"
>
pair_style dipole
</A>
command. Only the 1st component of the shape is used since the
particles are assumed to be spherical.
</P>
<P>
Ellipsoids use the atom shape to compute a generalized inertia tensor.
For example, a shape setting of 3.0 1.0 1.0 defines a particle 3x
longer in x than in y or z and with a circular cross-section in yz.
Degenerate ellipsoids which are spherical can be defined by setting
all 3 shape components the same.
</P>
<P>
If you define a
<A
HREF =
"atom_style.html"
>
hybrid atom style
</A>
which includes one
(or more) sub-styles which require per-type shape and one (or more)
sub-styles which require per-atom shape, then you must define both.
If the per-atom diameter is set to 0.0, the per-type shape is used.
If the per-atom diameter is non-zero, then the per-type shape is
ignored.
</P>
<P><B>
Restrictions:
</B>
</P>
<P>
This command must come after the simulation box is defined by a
<A
HREF =
"read_data.html"
>
read_data
</A>
,
<A
HREF =
"read_restart.html"
>
read_restart
</A>
, or
<A
HREF =
"create_box.html"
>
create_box
</A>
command.
</P>
<P>
All shapes must be defined before a simulation is run (if the atom
style requires shapes be set).
</P>
<P><B>
Related commands:
</B>
none
</P>
<P><B>
Default:
</B>
none
</P>
</HTML>
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