2007-06-20 21:15:18 +08:00
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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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<HR>
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2013-06-06 23:19:12 +08:00
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<H3>pair_style lj/cut/dipole/cut command
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2007-06-20 21:15:18 +08:00
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</H3>
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2013-06-06 23:19:12 +08:00
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<H3>pair_style lj/cut/dipole/cut/gpu command
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2012-08-21 21:54:09 +08:00
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</H3>
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2013-06-06 23:19:12 +08:00
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<H3>pair_style lj/cut/dipole/cut/omp command
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2011-10-07 01:32:51 +08:00
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</H3>
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2013-06-06 23:19:12 +08:00
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<H3>pair_style lj/sf/dipole/sf command
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2011-08-09 05:51:11 +08:00
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</H3>
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2013-06-06 23:19:12 +08:00
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<H3>pair_style lj/sf/dipole/sf/gpu command
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2012-08-21 21:54:09 +08:00
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</H3>
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2013-06-06 23:19:12 +08:00
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<H3>pair_style lj/sf/dipole/sf/omp command
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</H3>
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<H3>pair_style lj/cut/dipole/long command
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</H3>
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<H3>pair_style lj/long/dipole/long command
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2011-10-07 01:32:51 +08:00
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</H3>
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2007-06-20 21:15:18 +08:00
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<P><B>Syntax:</B>
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</P>
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2013-06-07 00:04:40 +08:00
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<PRE>pair_style lj/cut/dipole/cut cutoff (cutoff2)
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pair_style lj/sf/dipole/sf cutoff (cutoff2)
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pair_style lj/cut/dipole/long cutoff (cutoff2)
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pair_style lj/long/dipole/long flag_lj flag_coul cutoff (cutoff2)
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2007-06-20 21:15:18 +08:00
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</PRE>
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2013-06-06 23:19:12 +08:00
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<UL><LI>cutoff = global cutoff LJ (and Coulombic if only 1 arg) (distance units)
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<LI>cutoff2 = global cutoff for Coulombic and dipole (optional) (distance units)
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<LI>flag_lj = <I>long</I> or <I>cut</I> or <I>off</I>
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<PRE> <I>long</I> = use long-range damping on dispersion 1/r^6 term
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<I>cut</I> = use a cutoff on dispersion 1/r^6 term
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<I>off</I> = omit disperion 1/r^6 term entirely
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</PRE>
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<LI>flag_coul = <I>long</I> or <I>off</I>
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<PRE> <I>long</I> = use long-range damping on Coulombic 1/r and point-dipole terms
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<I>off</I> = omit Coulombic and point-dipole terms entirely
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2011-08-09 05:51:11 +08:00
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</PRE>
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2013-06-06 23:19:12 +08:00
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2007-06-20 21:15:18 +08:00
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</UL>
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<P><B>Examples:</B>
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</P>
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2013-06-06 23:19:12 +08:00
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<PRE>pair_style lj/cut/dipole/cut 10.0
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2007-06-20 21:15:18 +08:00
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pair_coeff * * 1.0 1.0
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pair_coeff 2 3 1.0 1.0 2.5 4.0
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</PRE>
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2013-06-06 23:19:12 +08:00
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<PRE>pair_style lj/sf/dipole/sf 9.0
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pair_coeff * * 1.0 1.0
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pair_coeff 2 3 1.0 1.0 2.5 4.0
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</PRE>
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<PRE>pair_style lj/cut/dipole/long 10.0
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pair_coeff * * 1.0 1.0
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pair_coeff 2 3 1.0 1.0 2.5 4.0
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</PRE>
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<PRE>pair_style lj/long/dipole/long long long 3.5 10.0
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2011-08-09 05:51:11 +08:00
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pair_coeff * * 1.0 1.0
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pair_coeff 2 3 1.0 1.0 2.5 4.0
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</PRE>
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2007-06-20 21:15:18 +08:00
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<P><B>Description:</B>
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</P>
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2013-06-06 23:19:12 +08:00
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<P>Style <I>lj/cut/dipole/cut</I> computes interactions between pairs of particles
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2007-06-20 21:15:18 +08:00
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that each have a charge and/or a point dipole moment. In addition to
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the usual Lennard-Jones interaction between the particles (Elj) the
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charge-charge (Eqq), charge-dipole (Eqp), and dipole-dipole (Epp)
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interactions are computed by these formulas for the energy (E), force
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(F), and torque (T) between particles I and J.
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</P>
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<CENTER><IMG SRC = "Eqs/pair_dipole.jpg">
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</CENTER>
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<P>where qi and qj are the charges on the two particles, pi and pj are
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the dipole moment vectors of the two particles, r is their separation
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distance, and the vector r = Ri - Rj is the separation vector between
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the two particles. Note that Eqq and Fqq are simply Coulombic energy
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and force, Fij = -Fji as symmetric forces, and Tij != -Tji since the
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torques do not act symmetrically. These formulas are discussed in
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<A HREF = "#Allen">(Allen)</A> and in <A HREF = "#Toukmaji">(Toukmaji)</A>.
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</P>
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2013-06-06 23:19:12 +08:00
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<P>Style <I>lj/sf/dipole/sf</I> computes "shifted-force" interactions between
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pairs of particles that each have a charge and/or a point dipole
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moment. In general, a shifted-force potential is a (sligthly) modified
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potential containing extra terms that make both the energy and its
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derivative go to zero at the cutoff distance; this removes
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(cutoff-related) problems in energy conservation and any numerical
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instability in the equations of motion <A HREF = "#Allen">(Allen)</A>. Shifted-force
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interactions for the Lennard-Jones (E_LJ), charge-charge (Eqq),
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charge-dipole (Eqp), dipole-charge (Epq) and dipole-dipole (Epp)
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potentials are computed by these formulas for the energy (E), force
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(F), and torque (T) between particles I and J:
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2011-08-09 05:51:11 +08:00
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</P>
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<CENTER><IMG SRC = "Eqs/pair_dipole_sf.jpg">
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</CENTER>
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2011-08-17 07:39:57 +08:00
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<CENTER><IMG SRC = "Eqs/pair_dipole_sf2.jpg">
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</CENTER>
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<P>where epsilon and sigma are the standard LJ parameters, r_c is the
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cutoff, qi and qj are the charges on the two particles, pi and pj are
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2011-08-09 05:51:11 +08:00
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the dipole moment vectors of the two particles, r is their separation
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distance, and the vector r = Ri - Rj is the separation vector between
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the two particles. Note that Eqq and Fqq are simply Coulombic energy
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and force, Fij = -Fji as symmetric forces, and Tij != -Tji since the
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torques do not act symmetrically. The shifted-force formula for the
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Lennard-Jones potential is reported in <A HREF = "#Stoddard">(Stoddard)</A>. The
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original (unshifted) formulas for the electrostatic potentials, forces
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and torques can be found in <A HREF = "#Price">(Price)</A>. The shifted-force
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electrostatic potentials have been obtained by applying equation 5.13
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of <A HREF = "#Allen">(Allen)</A>. The formulas for the corresponding forces and
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torques have been obtained by applying the 'chain rule' as in appendix
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C.3 of <A HREF = "#Allen">(Allen)</A>.
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</P>
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2007-06-20 21:15:18 +08:00
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<P>If one cutoff is specified in the pair_style command, it is used for
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both the LJ and Coulombic (q,p) terms. If two cutoffs are specified,
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they are used as cutoffs for the LJ and Coulombic (q,p) terms
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respectively.
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</P>
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2013-06-06 23:19:12 +08:00
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<P>Style <I>lj/cut/dipole/long</I> computes long-range point-dipole
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interactions as discussed in <A HREF = "#Toukmaji">(Toukmaji)</A>. Dipole-dipole,
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dipole-charge, and charge-charge interactions are all supported, along
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with the standard 12/6 Lennard-Jones interactions, which are computed
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with a cutoff. A <A HREF = "kspace_style.html">kspace_style</A> must be defined to
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use this pair style. Currently, only <A HREF = "kspace_style.html">kspace_style
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ewald/disp</A> support long-range point-dipole
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interactions.
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</P>
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<P>Style <I>lj/long/dipole/long</I> also computes point-dipole interactions as
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discussed in <A HREF = "#Toukmaji">(Toukmaji)</A>. Long-range dipole-dipole,
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dipole-charge, and charge-charge interactions are all supported, along
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2013-06-07 00:08:31 +08:00
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with the standard 12/6 Lennard-Jones interactions. LJ interactions
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can be cutoff or long-ranged.
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2013-06-06 23:19:12 +08:00
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</P>
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<P>For style <I>lj/long/dipole/long</I>, if <I>flag_lj</I> is set to <I>long</I>, no
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cutoff is used on the LJ 1/r^6 dispersion term. The long-range
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portion is calculated by using the <A HREF = "kspace_style.html">kspace_style
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ewald_disp</A> command. The specified LJ cutoff then
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determines which portion of the LJ interactions are computed directly
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by the pair potential versus which part is computed in reciprocal
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space via the Kspace style. If <I>flag_lj</I> is set to <I>cut</I>, the LJ
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interactions are simply cutoff, as with <A HREF = "pair_lj.html">pair_style
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2013-06-07 00:08:31 +08:00
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lj/cut</A>. If <I>flag_lj</I> is set to <I>off</I>, LJ interactions
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are not computed at all.
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</P>
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<P>If <I>flag_coul</I> is set to <I>long</I>, no cutoff is used on the Coulombic or
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dipole interactions. The long-range portion is calculated by using
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<I>ewald_disp</I> of the <A HREF = "kspace_style.html">kspace_style</A> command. If
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<I>flag_coul</I> is set to <I>off</I>, Coulombic and dipole interactions are not
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computed at all.
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2013-06-06 23:19:12 +08:00
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</P>
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2009-03-16 22:46:18 +08:00
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<P>Atoms with dipole moments should be integrated using the <A HREF = "fix_nve_sphere.html">fix
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nve/sphere update dipole</A> command to rotate the
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2013-06-06 23:19:12 +08:00
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dipole moments. The <I>omega</I> option on the <A HREF = "fix_langevin.html">fix
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langevin</A> command can be used to thermostat the
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rotational motion. The <A HREF = "compute_temp_sphere.html">compute temp/sphere</A>
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2009-03-16 22:46:18 +08:00
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command can be used to monitor the temperature, since it includes
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rotational degrees of freedom. The <A HREF = "atom_style.html">atom_style
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dipole</A> command should be used since it defines the
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point dipoles and their rotational state. The magnitude of the dipole
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moment for each type of particle can be defined by the
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<A HREF = "dipole.html">dipole</A> command or in the "Dipoles" section of the data
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file read in by the <A HREF = "read_data.html">read_data</A> command. Their initial
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orientation can be defined by the <A HREF = "set.html">set dipole</A> command or in
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the "Atoms" section of the data file.
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2007-06-20 21:15:18 +08:00
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</P>
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<P>The following coefficients must be defined for each pair of atoms
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types via the <A HREF = "pair_coeff.html">pair_coeff</A> command as in the examples
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above, or in the data file or restart files read by the
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<A HREF = "read_data.html">read_data</A> or <A HREF = "read_restart.html">read_restart</A>
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2007-06-25 22:36:36 +08:00
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commands, or by mixing as described below:
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2007-06-20 21:15:18 +08:00
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</P>
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<UL><LI>epsilon (energy units)
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<LI>sigma (distance units)
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<LI>cutoff1 (distance units)
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<LI>cutoff2 (distance units)
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</UL>
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<P>The latter 2 coefficients are optional. If not specified, the global
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LJ and Coulombic cutoffs specified in the pair_style command are used.
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If only one cutoff is specified, it is used as the cutoff for both LJ
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and Coulombic interactions for this type pair. If both coefficients
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are specified, they are used as the LJ and Coulombic cutoffs for this
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type pair.
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</P>
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2007-06-25 22:36:36 +08:00
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<HR>
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2011-12-14 04:35:35 +08:00
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<P>Styles with a <I>cuda</I>, <I>gpu</I>, <I>omp</I>, or <I>opt</I> suffix are functionally
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the same as the corresponding style without the suffix. They have
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been optimized to run faster, depending on your available hardware, as
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discussed in <A HREF = "Section_accelerate.html">Section_accelerate</A> of the
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manual. The accelerated styles take the same arguments and should
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produce the same results, except for round-off and precision issues.
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2011-10-07 01:32:51 +08:00
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</P>
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<P>These accelerated styles are part of the USER-CUDA, GPU, USER-OMP and OPT
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packages, respectively. They are only enabled if LAMMPS was built with
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those packages. See the <A HREF = "Section_start.html#start_3">Making LAMMPS</A>
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section for more info.
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</P>
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<P>You can specify the accelerated styles explicitly in your input script
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2012-01-28 07:39:14 +08:00
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by including their suffix, or you can use the <A HREF = "Section_start.html#start_7">-suffix command-line
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2011-10-07 01:32:51 +08:00
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switch</A> when you invoke LAMMPS, or you can
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use the <A HREF = "suffix.html">suffix</A> command in your input script.
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</P>
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2011-12-14 04:35:35 +08:00
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<P>See <A HREF = "Section_accelerate.html">Section_accelerate</A> of the manual for
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more instructions on how to use the accelerated styles effectively.
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2011-10-07 01:32:51 +08:00
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</P>
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<HR>
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2008-01-22 02:12:34 +08:00
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<P><B>Mixing, shift, table, tail correction, restart, rRESPA info</B>:
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2007-06-25 22:36:36 +08:00
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</P>
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<P>For atom type pairs I,J and I != J, the epsilon and sigma coefficients
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and cutoff distances for this pair style can be mixed. The default
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mix value is <I>geometric</I>. See the "pair_modify" command for details.
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</P>
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<P>For atom type pairs I,J and I != J, the A, sigma, d1, and d2
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coefficients and cutoff distance for this pair style can be mixed. A
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is an energy value mixed like a LJ epsilon. D1 and d2 are distance
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values and are mixed like sigma. The default mix value is
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<I>geometric</I>. See the "pair_modify" command for details.
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</P>
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2011-08-09 05:51:11 +08:00
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<P>This pair style does not support the <A HREF = "pair_modify.html">pair_modify</A>
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shift option for the energy of the Lennard-Jones portion of the pair
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interaction; such energy goes to zero at the cutoff by construction.
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2007-06-20 21:15:18 +08:00
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</P>
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2007-06-25 22:36:36 +08:00
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<P>The <A HREF = "pair_modify.html">pair_modify</A> table option is not relevant
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for this pair style.
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</P>
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<P>This pair style does not support the <A HREF = "pair_modify.html">pair_modify</A>
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tail option for adding long-range tail corrections to energy and
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pressure.
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</P>
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<P>This pair style writes its information to <A HREF = "restart.html">binary restart
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files</A>, so pair_style and pair_coeff commands do not need
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to be specified in an input script that reads a restart file.
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</P>
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2007-10-04 08:21:14 +08:00
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<P>This pair style can only be used via the <I>pair</I> keyword of the
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<A HREF = "run_style.html">run_style respa</A> command. It does not support the
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2007-10-12 07:09:49 +08:00
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<I>inner</I>, <I>middle</I>, <I>outer</I> keywords.
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2007-10-04 08:21:14 +08:00
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</P>
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2007-06-25 22:36:36 +08:00
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<P><B>Restrictions:</B>
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2007-06-20 21:15:18 +08:00
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</P>
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2013-06-06 23:19:12 +08:00
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<P>The <I>lj/cut/dipole/cut</I>, <I>lj/cut/dipole/long</I>, and
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<I>lj/long/dipole/long</I> styles are part of the DIPOLE package. They are
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only enabled if LAMMPS was built with that package. See the <A HREF = "Section_start.html#start_3">Making
|
2011-08-09 05:51:11 +08:00
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LAMMPS</A> section for more info.
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</P>
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2013-06-06 23:19:12 +08:00
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<P>The <I>lj/sf/dipole/sf</I> style is part of the USER-MISC package. It is
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only enabled if LAMMPS was built with that package. See the <A HREF = "Section_start.html#start_3">Making
|
2007-06-25 22:36:36 +08:00
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LAMMPS</A> section for more info.
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2007-06-20 21:15:18 +08:00
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</P>
|
2013-06-06 23:19:12 +08:00
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<P>Using dipole pair styles with <I>electron</I> <A HREF = "units.html">units</A> is not
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currently supported.
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</P>
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2007-06-20 21:15:18 +08:00
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<P><B>Related commands:</B>
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</P>
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2010-05-07 23:11:21 +08:00
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<P><A HREF = "pair_coeff.html">pair_coeff</A>
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2007-06-20 21:15:18 +08:00
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</P>
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<P><B>Default:</B> none
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</P>
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<HR>
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<A NAME = "Allen"></A>
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<P><B>(Allen)</B> Allen and Tildesley, Computer Simulation of Liquids,
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Clarendon Press, Oxford, 1987.
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</P>
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<A NAME = "Toukmaji"></A>
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<P><B>(Toukmaji)</B> Toukmaji, Sagui, Board, and Darden, J Chem Phys, 113,
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10913 (2000).
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</P>
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2011-08-09 05:51:11 +08:00
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<A NAME = "Stoddard"></A>
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<P><B>(Stoddard)</B> Stoddard and Ford, Phys Rev A, 8, 1504 (1973).
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</P>
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<A NAME = "Price"></A>
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<P><B>(Price)</B> Price, Stone and Alderton, Mol Phys, 52, 987 (1984).
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</P>
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2007-06-20 21:15:18 +08:00
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</HTML>
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