2006-09-22 00:22:34 +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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<H3>pair_style lj/cut command
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</H3>
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2011-06-09 05:46:03 +08:00
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<H3>pair_style lj/cut/cuda command
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</H3>
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<H3>pair_style lj/cut/experimental/cuda command
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</H3>
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2009-08-13 00:45:55 +08:00
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<H3>pair_style lj/cut/gpu command
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</H3>
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2007-02-10 05:40:32 +08:00
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<H3>pair_style lj/cut/opt command
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</H3>
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2006-09-22 00:22:34 +08:00
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<H3>pair_style lj/cut/coul/cut command
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</H3>
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2011-06-09 05:46:03 +08:00
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<H3>pair_style lj/cut/coul/cut/cuda command
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</H3>
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2010-11-23 08:51:42 +08:00
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<H3>pair_style lj/cut/coul/cut/gpu command
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</H3>
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2006-09-22 00:22:34 +08:00
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<H3>pair_style lj/cut/coul/debye command
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</H3>
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2011-06-09 05:46:03 +08:00
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<H3>pair_style lj/cut/coul/debye/cuda command
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</H3>
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2006-09-22 00:22:34 +08:00
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<H3>pair_style lj/cut/coul/long command
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</H3>
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2011-06-09 05:46:03 +08:00
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<H3>pair_style lj/cut/coul/long/cuda command
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</H3>
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2010-11-23 08:51:42 +08:00
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<H3>pair_style lj/cut/coul/long/gpu command
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</H3>
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2006-09-22 00:22:34 +08:00
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<H3>pair_style lj/cut/coul/long/tip4p command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>pair_style style args
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</PRE>
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2011-06-09 05:26:06 +08:00
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<UL><LI>style = <I>lj/cut</I> or <I>lj/cut/coul/cut</I> or <I>lj/cut/coul/debye</I> or <I>lj/cut/coul/long</I> or <I>lj/cut/coul/long/tip4p</I>
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2006-09-22 00:22:34 +08:00
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<LI>args = list of arguments for a particular style
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</UL>
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<PRE> <I>lj/cut</I> args = cutoff
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cutoff = global cutoff for Lennard Jones interactions (distance units)
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<I>lj/cut/coul/cut</I> args = cutoff (cutoff2)
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cutoff = global cutoff for LJ (and Coulombic if only 1 arg) (distance units)
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cutoff2 = global cutoff for Coulombic (optional) (distance units)
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<I>lj/cut/coul/debye</I> args = kappa cutoff (cutoff2)
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kappa = Debye length (inverse distance units)
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cutoff = global cutoff for LJ (and Coulombic if only 1 arg) (distance units)
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cutoff2 = global cutoff for Coulombic (optional) (distance units)
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<I>lj/cut/coul/long</I> args = cutoff (cutoff2)
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cutoff = global cutoff for LJ (and Coulombic if only 1 arg) (distance units)
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cutoff2 = global cutoff for Coulombic (optional) (distance units)
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<I>lj/cut/coul/long/tip4p</I> args = otype htype btype atype qdist cutoff (cutoff2)
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otype,htype = atom types for TIP4P O and H
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btype,atype = bond and angle types for TIP4P waters
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qdist = distance from O atom to massless charge (distance units)
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cutoff = global cutoff for LJ (and Coulombic if only 1 arg) (distance units)
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cutoff2 = global cutoff for Coulombic (optional) (distance units)
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</PRE>
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<P><B>Examples:</B>
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</P>
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<PRE>pair_style lj/cut 2.5
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pair_coeff * * 1 1
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pair_coeff 1 1 1 1.1 2.8
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</PRE>
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<PRE>pair_style lj/cut/coul/cut 10.0
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pair_style lj/cut/coul/cut 10.0 8.0
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pair_coeff * * 100.0 3.0
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pair_coeff 1 1 100.0 3.5 9.0
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pair_coeff 1 1 100.0 3.5 9.0 9.0
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</PRE>
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<PRE>pair_style lj/cut/coul/debye 1.5 3.0
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pair_style lj/cut/coul/debye 1.5 2.5 5.0
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pair_coeff * * 1.0 1.0
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pair_coeff 1 1 1.0 1.5 2.5
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pair_coeff 1 1 1.0 1.5 2.5 5.0
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</PRE>
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<PRE>pair_style lj/cut/coul/long 10.0
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pair_style lj/cut/coul/long 10.0 8.0
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pair_coeff * * 100.0 3.0
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pair_coeff 1 1 100.0 3.5 9.0
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</PRE>
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<PRE>pair_style lj/cut/coul/long/tip4p 1 2 7 8 0.3 12.0
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pair_style lj/cut/coul/long/tip4p 1 2 7 8 0.3 12.0 10.0
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pair_coeff * * 100.0 3.0
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pair_coeff 1 1 100.0 3.5 9.0
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</PRE>
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<P><B>Description:</B>
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</P>
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2007-10-04 08:21:14 +08:00
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<P>The <I>lj/cut</I> styles compute the standard 12/6 Lennard-Jones potential,
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2006-09-22 00:22:34 +08:00
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given by
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</P>
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<CENTER><IMG SRC = "Eqs/pair_lj.jpg">
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</CENTER>
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<P>Rc is the cutoff.
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</P>
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<P>Style <I>lj/cut/coul/cut</I> adds a Coulombic pairwise interaction given by
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</P>
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<CENTER><IMG SRC = "Eqs/pair_coulomb.jpg">
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</CENTER>
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<P>where C is an energy-conversion constant, Qi and Qj are the charges on
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the 2 atoms, and epsilon is the dielectric constant which can be set
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by the <A HREF = "dielectric.html">dielectric</A> command. If one cutoff is
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specified in the pair_style command, it is used for both the LJ and
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Coulombic terms. If two cutoffs are specified, they are used as
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cutoffs for the LJ and Coulombic terms respectively.
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</P>
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<P>Style <I>lj/cut/coul/debye</I> adds an additional exp() damping factor
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to the Coulombic term, given by
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</P>
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<CENTER><IMG SRC = "Eqs/pair_debye.jpg">
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</CENTER>
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<P>where kappa is the Debye length. This potential is another way to
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mimic the screening effect of a polar solvent.
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</P>
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<P>Style <I>lj/cut/coul/long</I> computes the same Coulombic interactions as
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style <I>lj/cut/coul/cut</I> except that an additional damping factor is
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applied to the Coulombic term so it can be used in conjunction with
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the <A HREF = "kspace_style.html">kspace_style</A> command and its <I>ewald</I> or <I>pppm</I>
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option. The Coulombic cutoff specified for this style means that
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pairwise interactions within this distance are computed directly;
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2007-10-03 05:55:02 +08:00
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interactions outside that distance are computed in reciprocal space.
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2006-09-22 00:22:34 +08:00
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</P>
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<P>Style <I>lj/cut/coul/long/tip4p</I> implements the TIP4P water model of
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<A HREF = "#Jorgensen">(Jorgensen)</A>, which introduces a massless site located a
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short distance away from the oxygen atom along the bisector of the HOH
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angle. The atomic types of the oxygen and hydrogen atoms, the bond
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and angle types for OH and HOH interactions, and the distance to the
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2007-02-10 05:40:32 +08:00
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massless charge site are specified as pair_style arguments.
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</P>
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<P>IMPORTANT NOTE: For each TIP4P water molecule in your system, the atom
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IDs for the O and 2 H atoms must be consecutive, with the O atom
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first. This is to enable LAMMPS to "find" the 2 H atoms associated
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with each O atom. For example, if the atom ID of an O atom in a TIP4P
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water molecule is 500, then its 2 H atoms must have IDs 501 and 502.
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</P>
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<P>See the <A HREF = "Section_howto.html#4_8">howto section</A> for more information on
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how to use the TIP4P pair style.
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2006-09-22 00:22:34 +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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2006-09-22 00:22:34 +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>Note that sigma is defined in the LJ formula as the zero-crossing
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distance for the potential, not as the energy minimum at 2^(1/6)
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sigma.
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</P>
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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. You cannot specify 2 cutoffs for style <I>lj/cut</I>, since it
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has no Coulombic terms.
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</P>
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<P>For <I>lj/cut/coul/long</I> and <I>lj/cut/coul/long/tip4p</I> only the LJ cutoff
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can be specified since a Coulombic cutoff cannot be specified for an
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individual I,J type pair. All type pairs use the same global
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Coulombic cutoff specified in the pair_style command.
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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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2011-06-09 05:26:06 +08:00
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<P>Styles with a <I>cuda</I>, <I>gpu</I>, or <I>opt</I> suffix are functionally the same
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as the corresponding style without the suffix. They have been
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optimized to run faster, depending on your available hardware, as
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discussed in <A HREF = "Section_accelerate.html">this section</A> of the manual.
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The accelerated styles take the same arguments and should produce the
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same results, except for round-off and precision issues.
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</P>
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<P>These accelerated styles are part of the "user-cuda", "gpu", 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#2_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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by including their suffix, or you can use the <A HREF = "Section_start.html#2_6">-suffix command-line
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switch</A> when you invoke LAMMPS, or you can use
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the <A HREF = "suffix.html">suffix</A> command in your input script.
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</P>
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<P>See <A HREF = "Section_accelerate.html">this section</A> of the manual for more
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instructions on how to use the accelerated styles effectively.
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2009-08-13 00:45:55 +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 distance for all of the lj/cut pair styles can be mixed.
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The default mix value is <I>geometric</I>. See the "pair_modify" command
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for details.
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</P>
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<P>All of the lj/cut pair styles support the
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<A HREF = "pair_modify.html">pair_modify</A> shift option for the energy of the
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Lennard-Jones portion of the pair interaction.
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</P>
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<P>The <I>lj/cut/coul/long</I> and <I>lj/cut/coul/long/tip4p</I> pair styles
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support the <A HREF = "pair_modify.html">pair_modify</A> table option since they can
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tabulate the short-range portion of the long-range Coulombic
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interaction.
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</P>
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<P>All of the lj/cut pair styles support the
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<A HREF = "pair_modify.html">pair_modify</A> tail option for adding a long-range
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2010-12-02 23:33:15 +08:00
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tail correction to the energy and pressure for the Lennard-Jones
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2007-06-25 22:36:36 +08:00
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portion of the pair interaction.
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</P>
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<P>All of the lj/cut pair styles write their information to <A HREF = "restart.html">binary
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restart files</A>, so pair_style and pair_coeff commands do
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not need 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>The lj/cut and lj/cut/coul/long pair styles support the use of the
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<I>inner</I>, <I>middle</I>, and <I>outer</I> keywords of the <A HREF = "run_style.html">run_style
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respa</A> command, meaning the pairwise forces can be
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partitioned by distance at different levels of the rRESPA hierarchy.
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The other styles only support the <I>pair</I> keyword of run_style respa.
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See the <A HREF = "run_style.html">run_style</A> command for details.
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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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2006-09-22 00:22:34 +08:00
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<P><B>Restrictions:</B>
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</P>
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2007-06-25 22:36:36 +08:00
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<P>The <I>lj/cut/coul/long</I> and <I>lj/cut/coul/long/tip4p</I> styles are part of
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2011-06-09 05:26:06 +08:00
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the "kspace" package. They are only enabled if LAMMPS was built with
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those packages. See the <A HREF = "Section_start.html#2_3">Making LAMMPS</A>
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section for more info. Note that the kspace package is installed by
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default.
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2006-09-22 00:22:34 +08:00
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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 = "pair_coeff.html">pair_coeff</A>
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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 = "Jorgensen"></A>
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<P><B>(Jorgensen)</B> Jorgensen, Chandrasekhar, Madura, Impey, Klein, J Chem
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Phys, 79, 926 (1983).
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</P>
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</HTML>
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