forked from lijiext/lammps
100 lines
3.8 KiB
Plaintext
100 lines
3.8 KiB
Plaintext
"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
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:link(lws,http://lammps.sandia.gov)
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:link(ld,Manual.html)
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:link(lc,Section_commands.html#comm)
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:line
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shape command :h3
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[Syntax:]
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shape I x y z :pre
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I = atom type (see asterisk form below)
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x = x diameter (distance units)
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y = y diameter (distance units)
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z = z diameter (distance units) :ul
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[Examples:]
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shape 1 1.0 1.0 1.0
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shape * 3.0 1.0 1.0
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shape 2* 3.0 1.0 1.0 :pre
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[Description:]
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Set the shape for all atoms of one or more atom types. In LAMMPS,
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particles that have a finite size are said to have a "shape", as
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opposed to being a point mass. The shape can be spherical or
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aspherical, depending on whether the 3 shape values are the same or
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different. Shape values can also be set in the
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"read_data"_read_data.html data file using the "Shapes" keyword. See
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the "units"_units.html command for what distance units to use.
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The I index can be specified in one of two ways. An explicit numeric
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value can be used, as in the 1st example above. Or a wild-card
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asterisk can be used to set the shape for multiple atom types. This
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takes the form "*" or "*n" or "n*" or "m*n". If N = the number of
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atom types, then an asterisk with no numeric values means all types
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from 1 to N. A leading asterisk means all types from 1 to n
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(inclusive). A trailing asterisk means all types from n to N
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(inclusive). A middle asterisk means all types from m to n
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(inclusive).
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A line in a "data file"_read_data.html that follows the "Shapes"
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keyword specifies shape using the same format as the arguments of the
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shape command in an input script, except that no wild-card asterisk
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can be used. For example, under the "Shapes" section of a data file,
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the line that corresponds to the 1st example above would be listed as
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1 1.0 1.0 1.0 :pre
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The shape values can be set to all 0.0, which means that atoms of that
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type are point particles and not finite-size particles. Some pair
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styles and fixes and computes that operate on finite-size particles
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allow for a mixture of finite-size and point particles. See the doc
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pages of individual commands for details.
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Note that the shape command can only be used if the "atom
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style"_atom_style.html requires per-type atom shape to be set.
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Currently, only the {colloid}, {dipole}, and {ellipsoid} styles do.
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The {granular} and {peri} styles also define finite-size spherical
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particles, but their size is set on a per-particle basis. These are
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are defined in the data file read by the "read_data"_read_data.html
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command, or set to default values by the
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"create_atoms"_create_atoms.html command, or set to new values by the
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"set diameter"_set.html command.
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Dipoles use the atom shape to compute a moment of inertia for
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rotational energy. See the "pair_style dipole"_pair_dipole.html
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command. Only the 1st component of the shape is used since the
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particles are assumed to be spherical.
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Ellipsoids use the atom shape to compute a generalized inertia tensor.
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For example, a shape setting of 3.0 1.0 1.0 defines a particle 3x
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longer in x than in y or z and with a circular cross-section in yz.
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Ellipsoids which are in fact spherical can be defined by setting all 3
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shape components the same.
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If you define a "hybrid atom style"_atom_style.html which includes one
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(or more) sub-styles which require per-type shape and one (or more)
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sub-styles which require per-atom diameter, then you must define both.
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However, in this case the per-type shape will be ignored; only the
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per-atom diameter will be used by LAMMPS. This means you cannot
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currently mix aspherical particles with per-atom diameter particles.
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[Restrictions:]
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This command must come after the simulation box is defined by a
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"read_data"_read_data.html, "read_restart"_read_restart.html, or
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"create_box"_create_box.html command.
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All shapes must be defined before a simulation is run (if the atom
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style requires shapes be set).
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[Related commands:] none
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[Default:] none
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