lammps/doc/atom_style.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

atom_style command :h3

[Syntax:]

atom_style style args :pre

style = {angle} or {atomic} or {bond} or {charge} or {dipole} or \
        {electron} or {ellipsoid} or {full} or {molecular} or \
	{peri} or {sphere} or {hybrid} :ul
  args = none for any style except {hybrid}
  {hybrid} args = list of one or more sub-styles :pre

[Examples:]

atom_style atomic
atom_style bond
atom_style full
atom_style hybrid charge bond :pre

[Description:]

Define what style of atoms to use in a simulation.  This determines
what attributes are associated with the atoms.  This command must be
used before a simulation is setup via a "read_data"_read_data.html,
"read_restart"_read_restart.html, or "create_box"_create_box.html
command.

Once a style is assigned, it cannot be changed, so use a style general
enough to encompass all attributes.  E.g. with style {bond}, angular
terms cannot be used or added later to the model.  It is OK to use a
style more general than needed, though it may be slightly inefficient.

The choice of style affects what quantities are stored by each atom,
what quantities are communicated between processors to enable forces
to be computed, and what quantities are listed in the data file read
by the "read_data"_read_data.html command.

These are the additional attributes of each style and the typical
kinds of physical systems they are used to model.  All styles store
coordinates, velocities, atom IDs and types.  See the
"read_data"_read_data.html, "create_atoms"_create_atoms.html, and
"set"_set.html commands for info on how to set these various
quantities.

{angle} | bonds and angles | bead-spring polymers with stiffness |
{atomic} | only the default values | coarse-grain liquids, solids, metals |
{bond} | bonds | bead-spring polymers |
{charge} | charge | atomic system with charges |
{dipole} | charge and dipole moment | system with dipolar particles |
{electron} | charge and spin and eradius | electronic force field |
{ellipsoid} | shape, quaternion for particle orientation, angular momentum | extended aspherical particles |
{full} | molecular + charge | bio-molecules |
{molecular} | bonds, angles, dihedrals, impropers | uncharged molecules |
{peri} | mass, volume | mesocopic Peridynamic models |
{sphere} | diameter, mass, angular velocity | granular models :tb(c=3,s=|)

All of the styles assign mass to particles on a per-type basis, using
the "mass"_mass.html command, except for the finite-size particle
styles discussed below.  They assign mass on a per-atom basis.

All of the styles define point particles, except the {sphere},
{ellipsoid}, {electron}, and {peri} styles, which define finite-size
particles.

For the {sphere} style, the particles are spheres and each stores a
per-particle diameter and mass.  For the {ellipsoid} style, the
particles are ellipsoids and each stores a per-particle shape vector
with the 3 diamters of the ellipsoid.  For the {electron} style, the
particles representing electrons are 3d Gaussians with a specified
position and bandwidth or uncertainty in position, which is
represented by the eradius = electron size.  For the {peri} style, the
particles are spherical and each stores a per-particle mass and
volume.

:line

Typically, simulations require only a single (non-hybrid) atom style.
If some atoms in the simulation do not have all the properties defined
by a particular style, use the simplest style that defines all the
needed properties by any atom.  For example, if some atoms in a
simulation are charged, but others are not, use the {charge} style.
If some atoms have bonds, but others do not, use the {bond} style.

The only scenario where the {hybrid} style is needed is if there is no
single style which defines all needed properties of all atoms.  For
example, if you want dipolar particles which will be torqued and
rotate, you would need to use "atom_style hybrid sphere dipole".  When
a hybrid style is used, atoms store and communicate the union of all
quantities implied by the individual styles.

LAMMPS can be extended with new atom styles; see "this
section"_Section_modify.html.

[Restrictions:]

This command cannot be used after the simulation box is defined by a
"read_data"_read_data.html or "create_box"_create_box.html command.

The {angle}, {bond}, {full}, and {molecular} styles are part of the
"molecular" package.  The {dipole} style is part of the "dipole"
package.  The {ellipsoid} style is part of the "asphere" package.  The
{peri} style is part of the "peri" package for Peridynamics.  The
{electron} style is part of the "user-eff" package for "electronic
force fields"_pair_eff.html.  They are only enabled if LAMMPS was
built with that package.  See the "Making
LAMMPS"_Section_start.html#2_3 section for more info.

[Related commands:]

"read_data"_read_data.html, "pair_style"_pair_style.html

[Default:]

atom_style atomic