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<CENTER><A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</A> - <A HREF = "Manual.html">LAMMPS Documentation</A> - <A HREF = "Section_commands.html#comm">LAMMPS Commands</A>
</CENTER>
<HR>
<H3>atom_style command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>atom_style style args
</PRE>
<UL><LI>style = <I>angle</I> or <I>atomic</I> or <I>bond</I> or <I>charge</I> or <I>colloid</I> or <I>dipole</I> or <I>electron</I> or <I>ellipsoid</I> or <I>full</I> or <I>granular</I> or <I>molecular</I> or <I>peri</I> or <I>hybrid</I>
</UL>
<PRE> args = none for any style except <I>hybrid</I>
<I>hybrid</I> args = list of one or more sub-styles
</PRE>
<P><B>Examples:</B>
</P>
<PRE>atom_style atomic
atom_style bond
atom_style full
atom_style hybrid charge bond
</PRE>
<P><B>Description:</B>
</P>
<P>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 <A HREF = "read_data.html">read_data</A>,
<A HREF = "read_restart.html">read_restart</A>, or <A HREF = "create_box.html">create_box</A>
command.
</P>
<P>Once a style is assigned, it cannot be changed, so use a style general
enough to encompass all attributes. E.g. with style <I>bond</I>, 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.
</P>
<P>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 <A HREF = "read_data.html">read_data</A> command.
</P>
<P>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
<A HREF = "read_data.html">read_data</A>, <A HREF = "create_atoms.html">create_atoms</A>, and
<A HREF = "set.html">set</A> commands for info on how to set these various
quantities.
</P>
<DIV ALIGN=center><TABLE BORDER=1 >
<TR><TD ><I>angle</I> </TD><TD > bonds and angles </TD><TD > bead-spring polymers with stiffness </TD></TR>
<TR><TD ><I>atomic</I> </TD><TD > only the default values </TD><TD > coarse-grain liquids, solids, metals </TD></TR>
<TR><TD ><I>bond</I> </TD><TD > bonds </TD><TD > bead-spring polymers </TD></TR>
<TR><TD ><I>charge</I> </TD><TD > charge </TD><TD > atomic system with charges </TD></TR>
<TR><TD ><I>colloid</I> </TD><TD > angular velocity </TD><TD > extended spherical particles </TD></TR>
<TR><TD ><I>dipole</I> </TD><TD > charge and dipole moment </TD><TD > atomic system with dipoles </TD></TR>
<TR><TD ><I>electron</I> </TD><TD > charge and spin and eradius </TD><TD > electronic force field </TD></TR>
<TR><TD ><I>ellipsoid</I> </TD><TD > quaternion for particle orientation, angular momentum </TD><TD > extended aspherical particles </TD></TR>
<TR><TD ><I>full</I> </TD><TD > molecular + charge </TD><TD > bio-molecules </TD></TR>
<TR><TD ><I>granular</I> </TD><TD > diameter, density, angular velocity </TD><TD > granular models </TD></TR>
<TR><TD ><I>molecular</I> </TD><TD > bonds, angles, dihedrals, impropers </TD><TD > uncharged molecules </TD></TR>
<TR><TD ><I>peri</I> </TD><TD > density, volume </TD><TD > mesocopic Peridynamic models
</TD></TR></TABLE></DIV>
<P>All of the styles define point particles, except the <I>colloid</I>,
<I>dipole</I>, <I>electron</I>, <I>ellipsoid</I>, <I>granular</I>, and <I>peri</I> styles,
which define finite-size particles. For <I>colloid</I>, <I>dipole</I>, and
<I>ellipsoid</I> systems, the <A HREF = "shape.html">shape</A> command is used to specify
the size and shape of particles on a per-type basis, which is
spherical for <I>colloid</I> and <I>dipole</I> particles and spherical or
aspherical for <I>ellipsoid</I> particles. For <I>granular</I> systems, the
particles are spherical and each has a per-particle specified
diameter. For <I>peri</I> systems, the particles are spherical and each
has a per-particle specified volume. For <I>electron</I> systems, the
particles representing electrons are three dimensional Gaussians with
a specified position and bandwidth or uncertainty in position, which
is represented by the eradius = electron size.
</P>
<P>All of the styles assign mass to particles on a per-type basis, using
the <A HREF = "mass.html">mass</A> command, except the <I>granular</I> and <I>peri</I> styles
which assign mass on a per-particle basis. For <I>granular</I> systems,
the specified diameter and density are used to calculate each
particle's mass. For <I>peri</I> systems, the speficied volume and density
are used to calculate each particle's mass.
</P>
<HR>
<P>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 <I>charge</I> style.
If some atoms have bonds, but others do not, use the <I>bond</I> style.
</P>
<P>The only scenario where the <I>hybrid</I> 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.
</P>
<P>LAMMPS can be extended with new atom styles; see <A HREF = "Section_modify.html">this
section</A>.
</P>
<P><B>Restrictions:</B>
</P>
<P>This command cannot be used after the simulation box is defined by a
<A HREF = "read_data.html">read_data</A> or <A HREF = "create_box.html">create_box</A> command.
</P>
<P>The <I>angle</I>, <I>bond</I>, <I>full</I>, and <I>molecular</I> styles are part of the
"molecular" package. The <I>granular</I> style is part of the "granular"
package. The <I>colloid</I> style is part of the "colloid" package. The
<I>dipole</I> style is part of the "dipole" package. The <I>ellipsoid</I> style
is part of the "asphere" package. The <I>peri</I> style is part of the
"peri" package for Peridynamics. The <I>electron</I> style is part of the
"user-eff" package for <A HREF = "pair_eff.html">electronic force fields</A>. They
are only enabled if LAMMPS was built with that package. See the
<A HREF = "Section_start.html#2_3">Making LAMMPS</A> section for more info.
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "read_data.html">read_data</A>, <A HREF = "pair_style.html">pair_style</A>
</P>
<P><B>Default:</B>
</P>
<P>atom_style atomic
</P>
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