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### atom_style command

Syntax:

    atom_style style args

- style = angle or atomic or bond or charge or colloid or dipole or ellipsoid or full or granular or molecular or peri or hybrid

      args = none for any style except hybrid
      hybrid args = list of one or more sub-styles

Examples:

    atom_style atomic
    atom_style bond
    atom_style full
    atom_style hybrid charge bond

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_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
bond | bonds | bead-spring polymers
charge | charge | atomic system with charges
colloid | angular velocity | extended spherical particles
dipole | charge and dipole moment | atomic system with dipoles
ellipsoid | quaternion for particle orientation, angular momentum | extended aspherical particles
full | molecular + charge | bio-molecules
granular | diameter, density, angular velocity | granular models
molecular | bonds, angles, dihedrals, impropers | uncharged molecules
peri | density, volume | mesocopic Peridynamic models

All of the styles define point particles, except the colloid, dipole, ellipsoid, granular, and peri styles, which define finite-size particles. For colloid, dipole, and ellipsoid systems, the shape command is used to specify the size and shape of particles on a per-type basis, which is spherical for colloid and dipole particles and spherical or aspherical for ellipsoid particles. For granular systems, the particles are spherical and each has a per-particle specified diameter. For peri systems, the particles are spherical and each has a per-particle specified volume.

All of the styles assign mass to particles on a per-type basis, using the mass command, except the granular and peri styles which assign mass on a per-particle basis. For granular systems, the specified diameter and density are used to calculate each particle's mass. For peri systems, the speficied volume and density are used to calculate each particle's mass.

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 colloidal particles with charge, you would need to use "atom_style hybrid colloid charge". 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.

Restrictions:

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 granular style is part of the "granular" package. The colloid style is part of the "colloid" 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. They are only enabled if LAMMPS was built with that package. See the Making LAMMPS section for more info.

Related commands:

read_data, pair_style

Default:

atom_style atomic