forked from lijiext/lammps
100 lines
4.1 KiB
HTML
100 lines
4.1 KiB
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<HTML>
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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>
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<H3>atom_style command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>atom_style style args
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</PRE>
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<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>hybrid</I>
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</UL>
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<PRE> args = none for any style except <I>hybrid</I>
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<I>hybrid</I> args = list of one or more sub-styles
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</PRE>
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<P><B>Examples:</B>
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</P>
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<PRE>atom_style atomic
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atom_style bond
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atom_style full
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atom_style hybrid charge bond
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>Define what style of atoms to use in a simulation. This determines
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what attributes are associated with the atoms. This command must be
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used before a simulation is setup via a <A HREF = "read_data.html">read_data</A>,
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<A HREF = "read_restart.html">read_restart</A>, or <A HREF = "create_box.html">create_box</A>
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command.
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</P>
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<P>Once a style is assigned, it cannot be changed, so use a style general
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enough to encompass all attributes. E.g. with style <I>bond</I>, angular
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terms cannot be used or added later to the model. It is OK to use a
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style more general than needed, though it may be slightly inefficient.
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</P>
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<P>The choice of style affects what quantities are stored by each atom,
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what quantities are communicated between processors to enable forces
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to be computed, and what quantities are listed in the data file read
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by the <A HREF = "read_data.html">read_data</A> command.
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</P>
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<P>These are the attributes of each style. All styles store coordinates,
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velocities, atom IDs and types.
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</P>
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<UL><LI><I>angle</I> = bonds and angles - e.g. bead-spring polymers with stiffness
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<LI><I>atomic</I> = only the default values
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<LI><I>bond</I> = bonds - e.g. bead-spring polymers
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<LI><I>charge</I> = charge
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<LI><I>dipole</I> = charge and dipole moment
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<LI><I>dpd</I> = default values, also communicates velocities
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<LI><I>ellipsoid</I> = quaternion for particle orientation, angular velocity/momentum
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<LI><I>full</I> = molecular + charge - e.g. biomolecules, charged polymers
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<LI><I>granular</I> = granular atoms with rotational properties
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<LI><I>molecular</I> = bonds, angles, dihedrals, impropers - e.g. all-atom polymers
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</UL>
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<P>Typically, simulations require only a single (non-hybrid) atom style.
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If some atoms in the simulation do not have all the properties defined
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by a particular style, use the simplest style that defines all the
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needed properties by any atom. For example, if some atoms in a
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simulation are charged, but others are not, use the <I>charge</I> style.
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If some atoms have bonds, but others do not, use the <I>bond</I> style.
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The only scenario where the <I>hybrid</I> style is needed is if there is no
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single style which defines all needed properties of all atoms.
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E.g. if you want charged DPD particles, you would need to use
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"atom_style hybrid dpd charge". When a hybrid style is used, atoms
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store and communicate the union of all quantities implied by the
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individual styles.
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</P>
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<P>LAMMPS can be extended with new atom styles; see <A HREF = "Section_modify.html">this
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section</A>.
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</P>
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<P><B>Restrictions:</B>
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</P>
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<P>This command cannot be used after the simulation box is defined by a
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<A HREF = "read_data.html">read_data</A> or <A HREF = "create_box.html">create_box</A> command.
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</P>
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<P>The <I>angle</I>, <I>bond</I>, <I>full</I>, and <I>molecular</I> styles are part of the
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"molecular" package. The <I>granular</I> style is part of the "granular"
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package. The <I>dpd</I> style is part of the "dpd" package. The <I>dipole</I>
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style is part of the "dipole" package. The <I>ellipsoid</I> style is part
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of the "ellipsoid" package. They are only enabled if LAMMPS was built
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with that package. See the <A HREF = "Section_start.html#2_3">Making LAMMPS</A>
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section for more info.
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</P>
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<P><B>Related commands:</B>
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</P>
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<P><A HREF = "read_data.html">read_data</A>, <A HREF = "pair_style.html">pair_style</A>
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</P>
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<P><B>Default:</B>
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</P>
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<P>atom_style atomic
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</P>
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