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"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Section_commands.html#comm)
:line
shape command :h3
[Syntax:]
shape I x y z :pre
I = atom type (see asterisk form below)
x = x diameter (distance units)
y = y diameter (distance units)
z = z diameter (distance units) :ul
[Examples:]
shape 1 1.0 1.0 1.0
shape * 3.0 1.0 1.0
shape 2* 3.0 1.0 1.0 :pre
[Description:]
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
"read_data"_read_data.html data file using the "Shapes" keyword. See
the "units"_units.html command for what distance units to use.
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).
A line in a "data file"_read_data.html 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
1 1.0 1.0 1.0 :pre
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.
Note that the shape command can only be used if the "atom
style"_atom_style.html requires per-type atom shape to be set.
Currently, only the {dipole} and {ellipsoid} styles do. The
{granular} and {peri} 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 "read_data"_read_data.html command, or set
to default values by the "create_atoms"_create_atoms.html command, or
set to new values by the "set diamter"_set.html command.
Dipoles use the atom shape to compute a moment of inertia for
rotational energy. See the "pair_style dipole"_pair_dipole.html
command. Only the 1st component of the shape is used since the
particles are assumed to be spherical.
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.
If you define a "hybrid atom style"_atom_style.html 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.
[Restrictions:]
This command must come after the simulation box is defined by a
"read_data"_read_data.html, "read_restart"_read_restart.html, or
"create_box"_create_box.html command.
All shapes must be defined before a simulation is run (if the atom
style requires shapes be set).
[Related commands:] none
[Default:] none
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