lammps/doc/shape.txt

"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:]

mass I x y z :pre

I = atom type (see asterik form below)
x = x diameter
y = y diameter
z = z diameter :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.  Shape values
can also be set in the "read_data"_read_data.html data file.  See the
"units"_units.html command for what distance units to use.

Currently, only "atom_style dipole"_atom_style.html and "atom_style
ellipsoid"_atom_style.html require that shapes be set.

Dipoles use the atom shape to compute a moment of inertia for
rotational energy.  Only the 1st componenet of the shape is used since
the particles are assumed to be spherical.  The value of the first
component should be the same as the Lennard-Jones sigma value defined
in the dipole pair potential, i.e. in "pair_style
dipole"_pair_dipole.html.

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.
Ellipsoids that are spherical can be defined by setting all 3 shape
components the same.

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
asterik can be used to set the mass for multiple atom types.  This
takes the form "*" or "*n" or "n*" or "m*n".  If N = the number of
atom types, then an asterik with no numeric values means all types
from 1 to N.  A leading asterik means all types from 1 to n
(inclusive).  A trailing asterik means all types from n to N
(inclusive).  A middle asterik means all types from m to n
(inclusive).

A line in a data file that specifies shape uses the same format as the
arguments of the shape command in an input script, except that no
wild-card asterik 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

[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