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_restart, or create_box 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 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, create_atoms, and set 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
body	mass, inertia moments, quaternion, angular momentum	arbitrary bodies
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, angular momentum	aspherical particles
full	molecular + charge	bio-molecules
line	end points, angular velocity	rigid bodies
meso	rho, e, cv	SPH particles
molecular	bonds, angles, dihedrals, impropers	uncharged molecules
peri	mass, volume	mesocopic Peridynamic models
sphere	diameter, mass, angular velocity	granular models
tri	corner points, angular momentum	rigid bodies
wavepacket	charge, spin, eradius, etag, cs_re, cs_im	AWPMD

IMPORTANT NOTE: It is possible to add some attributes, such as a molecule ID, to atom styles that do not have them via the fix property/atom command. This command also allows new custom attributes consisting of extra integer or floating-point values to be added to atoms. See the fix property/atom doc page for examples of cases where this is useful and details on how to initialize, access, and output the custom values.

All of the above styles define point particles, except the sphere, ellipsoid, electron, peri, wavepacket, line, tri, and body styles, which define finite-size particles. See Section_howto 14 for an overview of using finite-size particle models with LAMMPS.

All of the styles assign mass to particles on a per-type basis, using the mass command, except for the finite-size particle styles. They assign mass to individual particles on a per-particle basis.

For the sphere style, the particles are spheres and each stores a per-particle diameter and mass. If the diameter > 0.0, the particle is a finite-size sphere. If the diameter = 0.0, it is a point particle.

For the ellipsoid style, the particles are ellipsoids and each stores a flag which indicates whether it is a finite-size ellipsoid or a point particle. If it is an ellipsoid, it also stores a shape vector with the 3 diamters of the ellipsoid and a quaternion 4-vector with its orientation.

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.

The meso style is for smoothed particle hydrodynamics (SPH) particles which store a density (rho), energy (e), and heat capacity (cv).

The wavepacket style is similar to electron, but the electrons may consist of several Gaussian wave packets, summed up with coefficients cs= (cs_re,cs_im). Each of the wave packets is treated as a separate particle in LAMMPS, wave packets belonging to the same electron must have identical etag values.

For the line style, the particles are idealized line segments and each stores a per-particle mass and length and orientation (i.e. the end points of the line segment).

For the tri style, the particles are planar triangles and each stores a per-particle mass and size and orientation (i.e. the corner points of the triangle).

For the body style, the particles are arbitrary bodies with internal attributes defined by the "style" of the bodies, which is specified by the bstyle argument. Body particles can represent complex entities, such as surface meshes of discrete points, collections of sub-particles, deformable objects, etc.

The body doc page descibes the body styles LAMMPS currently supports, and provides more details as to the kind of body particles they represent. For all styles, each body particle stores moments of inertia and a quaternion 4-vector, so that its orientation and position can be time integrated due to forces and torques.

Note that there may be additional arguments required along with the bstyle specification, in the atom_style body command. These arguments are described in the body doc page.

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 rotate due to torque, 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 as well as new body styles; see this section.

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

The angle, bond, full, and molecular styles are part of the MOLECULAR package. The line and tri styles are part of the ASPHERE pacakge. The body style is part of the BODY package. The dipole style is part of the DIPOLE 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. The meso style is part of the USER-SPH package for smoothed particle hydrodyanmics (SPH). See this PDF guide to using SPH in LAMMPS. The wavepacket style is part of the USER-AWPMD package for the antisymmetrized wave packet MD method. They are only enabled if LAMMPS was built with that package. See the Making LAMMPS section for more info.

atom_style command