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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>dipole</I> or <I>dpd</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 attributes of each style. All styles store coordinates,
velocities, atom IDs and types.
</P>
<UL><LI><I>angle</I> = bonds and angles - e.g. bead-spring polymers with stiffness
<LI><I>atomic</I> = only the default values
<LI><I>bond</I> = bonds - e.g. bead-spring polymers
<LI><I>charge</I> = charge
<LI><I>dipole</I> = charge and dipole moment
<LI><I>dpd</I> = default values, also communicates velocities
<LI><I>ellipsoid</I> = quaternion for particle orientation, angular velocity/momentum
<LI><I>full</I> = molecular + charge - e.g. biomolecules, charged polymers
<LI><I>granular</I> = granular atoms with rotational properties
<LI><I>molecular</I> = bonds, angles, dihedrals, impropers - e.g. all-atom polymers
<LI><I>peri</I> = mass, volume - e.g. mesocopic Peridynamics
</UL>
<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.
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.
E.g. if you want charged DPD particles, you would need to use
"atom_style hybrid dpd 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>dpd</I> style is part of the "dpd" package. The <I>dipole</I>
style is part of the "dipole" package. The <I>ellipsoid</I> style is part
of the "ellipsoid" package. The <I>peri</I> style is part of the "peri"
package for Peridynamics. 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>
</HTML>
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