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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>pair_style dipole/cut command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>pair_style dipole/cut cutoff (cutoff2)
</PRE>
<UL><LI>cutoff = global cutoff LJ (and Coulombic if only 1 arg) (distance units)
<LI>cutoff2 = global cutoff for Coulombic (optional) (distance units)
</UL>
<P><B>Examples:</B>
</P>
<PRE>pair_style dipole/cut 10.0
pair_coeff * * 1.0 1.0
pair_coeff 2 3 1.0 1.0 2.5 4.0
</PRE>
<P><B>Description:</B>
</P>
<P>Style <I>dipole/cut</I> computes interactions bewteen pairs of particles
that each have a charge and/or a point dipole moment. In addition to
the usual Lennard-Jones interaction between the particles (Elj) the
charge-charge (Eqq), charge-dipole (Eqp), and dipole-dipole (Epp)
interactions are computed by these formulas for the energy (E), force
(F), and torque (T) between particles I and J.
</P>
<CENTER><IMG SRC = "Eqs/pair_dipole.jpg">
</CENTER>
<P>where qi and qj are the charges on the two particles, pi and pj are
the dipole moment vectors of the two particles, r is their separation
distance, and the vector r = Ri - Rj is the separation vector between
the two particles. Note that Eqq and Fqq are simply Coulombic energy
and force, Fij = -Fji as symmetric forces, and Tij != -Tji since the
torques do not act symmetrically. These formulas are discussed in
<A HREF = "#Allen">(Allen)</A> and in <A HREF = "#Toukmaji">(Toukmaji)</A>.
</P>
<P>If one cutoff is specified in the pair_style command, it is used for
both the LJ and Coulombic (q,p) terms. If two cutoffs are specified,
they are used as cutoffs for the LJ and Coulombic (q,p) terms
respectively.
</P>
<P>Use of this pair style requires the use of the <A HREF = "fix_nve_dipole.html">fix
nve/dipole</A> command to integrate rotation of the
dipole moments. Additionally, <A HREF = "atom_style.html">atom_style dipole</A>
should be used since it defines the point dipoles and their rotational
state. The magnitude of the dipole moment for each type of particle
can be defined by the <A HREF = "dipole.html">dipole</A> command or in the "Dipoles"
section of the data file read in by the <A HREF = "read_data.html">read_data</A>
command. Their initial orientation can be defined by the <A HREF = "set.html">set
dipole</A> command or in the "Atoms" section of the data file.
</P>
<P>The following coefficients must be defined for each pair of atoms
types via the <A HREF = "pair_coeff.html">pair_coeff</A> command as in the examples
above, or in the data file or restart files read by the
<A HREF = "read_data.html">read_data</A> or <A HREF = "read_restart.html">read_restart</A>
commands:
</P>
<UL><LI>epsilon (energy units)
<LI>sigma (distance units)
<LI>cutoff1 (distance units)
<LI>cutoff2 (distance units)
</UL>
<P>The latter 2 coefficients are optional. If not specified, the global
LJ and Coulombic cutoffs specified in the pair_style command are used.
If only one cutoff is specified, it is used as the cutoff for both LJ
and Coulombic interactions for this type pair. If both coefficients
are specified, they are used as the LJ and Coulombic cutoffs for this
type pair.
</P>
<P><B>Restrictions:</B>
</P>
<P>Can only be used if LAMMPS was built with the "dipole" package.
</P>
<P>The use of this potential requires additional fixes as described
above.
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "pair_coeff.html">pair_coeff</A>, <A HREF = "fix_nve_dipole.html">fix nve/dipole</A>,
<A HREF = "compute_temp_dipole.html">compute temp/dipole</A>
</P>
<P><B>Default:</B> none
</P>
<HR>
<A NAME = "Allen"></A>
<P><B>(Allen)</B> Allen and Tildesley, Computer Simulation of Liquids,
Clarendon Press, Oxford, 1987.
</P>
<A NAME = "Toukmaji"></A>
<P><B>(Toukmaji)</B> Toukmaji, Sagui, Board, and Darden, J Chem Phys, 113,
10913 (2000).
</P>
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