2007-10-03 07:26:51 +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 coul/cut command
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</H3>
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2011-10-07 01:32:51 +08:00
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<H3>pair_style coul/cut/omp command
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</H3>
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2008-01-04 09:38:02 +08:00
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<H3>pair_style coul/debye command
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</H3>
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2011-10-07 01:32:51 +08:00
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<H3>pair_style coul/debye/omp command
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</H3>
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2007-10-03 07:26:51 +08:00
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<H3>pair_style coul/long command
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</H3>
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2011-10-07 01:32:51 +08:00
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<H3>pair_style coul/long/omp command
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</H3>
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2011-12-02 23:47:30 +08:00
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<H3>pair_style coul/long/gpu command
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</H3>
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2011-12-13 23:56:58 +08:00
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<H3>pair_style coul/wolf command
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</H3>
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2012-01-07 01:38:57 +08:00
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<H3>pair_style coul/wolf/omp command
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</H3>
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2007-10-03 07:26:51 +08:00
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<P><B>Syntax:</B>
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</P>
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2011-12-02 23:47:30 +08:00
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<PRE>pair_style coul/cut cutoff
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2008-01-04 09:38:02 +08:00
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pair_style coul/debye kappa cutoff
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2011-08-24 07:10:45 +08:00
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pair_style coul/long cutoff
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2011-12-02 23:47:30 +08:00
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pair_style coul/long/gpu cutoff
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2011-12-13 23:56:58 +08:00
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pair_sytle coul/wolf alpha cutoff
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2011-12-02 23:47:30 +08:00
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</PRE>
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2008-01-04 09:38:02 +08:00
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<UL><LI>cutoff = global cutoff for Coulombic interactions
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<LI>kappa = Debye length (inverse distance units)
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2011-12-13 23:56:58 +08:00
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<LI>alpha = damping parameter (inverse distance units)
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2007-10-03 07:26:51 +08:00
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</UL>
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<P><B>Examples:</B>
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</P>
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<PRE>pair_style coul/cut 2.5
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pair_coeff * *
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pair_coeff 2 2 3.5
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</PRE>
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2008-01-04 09:38:02 +08:00
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<PRE>pair_style coul/debye 1.4 3.0
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pair_coeff * *
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pair_coeff 2 2 3.5
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</PRE>
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2007-10-03 07:26:51 +08:00
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<PRE>pair_style coul/long 10.0
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pair_coeff * *
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</PRE>
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2011-12-13 23:56:58 +08:00
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<P>pair_style coul/wolf 0.2 9.0
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pair_coeff * *
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</P>
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2007-10-03 07:26:51 +08:00
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<P><B>Description:</B>
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</P>
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<P>The <I>coul/cut</I> style computes the standard Coulombic interaction
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potential 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. The cutoff Rc truncates
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the interaction distance.
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</P>
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2008-01-04 09:38:02 +08:00
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<P>Style <I>coul/debye</I> adds an additional exp() damping factor to the
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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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2011-12-13 23:56:58 +08:00
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<P>Style <I>coul/wolf</I> computes Coulombic interactions via the Wolf
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summation method, described in <A HREF = "#Wolf">Wolf</A>, given by:
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</P>
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<CENTER><IMG SRC = "Eqs/pair_coul_wolf.jpg">
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</CENTER>
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<P>where <I>alpha</I> is the damping parameter, and erc() and erfc() are
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error-fuction and complementary error-function terms. This potential
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is essentially a short-range, spherically-truncated,
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charge-neutralized, shifted, pairwise <I>1/r</I> summation. With a
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manipulation of adding and substracting a self term (for i = j) to the
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first and second term on the right-hand-side, respectively, and a
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small enough <I>alpha</I> damping parameter, the second term shrinks and
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the potential becomes a rapidly-converging real-space summation. With
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a long enough cutoff and small enough alpha parameter, the energy and
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forces calcluated by the Wolf summation method approach those of the
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Ewald sum. So it is a means of getting effective long-range
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interactions with a short-range potential.
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</P>
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2007-10-03 07:26:51 +08:00
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<P>Style <I>coul/long</I> computes the same Coulombic interactions as style
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<I>coul/cut</I> except that an additional damping factor is applied so it
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can be used in conjunction with the <A HREF = "kspace_style.html">kspace_style</A>
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command and its <I>ewald</I> or <I>pppm</I> option. The Coulombic cutoff
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specified for this style means that pairwise interactions within this
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distance are computed directly; interactions outside that distance are
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computed in reciprocal space.
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</P>
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<P>These potentials are designed to be combined with other pair
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potentials via the <A HREF = "pair_hybrid.html">pair_style hybrid/overlay</A>
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command. This is because they have no repulsive core. Hence if they
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are used by themselves, there will be no repulsion to keep two
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oppositely charged particles from overlapping each other.
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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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commands, or by mixing as described below:
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</P>
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<UL><LI>cutoff (distance units)
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</UL>
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2008-01-04 09:38:02 +08:00
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<P>For <I>coul/cut</I> and <I>coul/debye</I>, the cutoff coefficient is optional.
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If it is not used (as in some of the examples above), the default
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global value specified in the pair_style command is used.
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2007-10-03 07:26:51 +08:00
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</P>
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<P>For <I>coul/long</I> no cutoff can be specified for an individual I,J type
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pair via the pair_coeff command. 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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<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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2011-08-24 05:11:24 +08:00
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</P>
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2011-10-07 01:32:51 +08:00
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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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2011-08-26 00:46:23 +08:00
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those packages. See the <A HREF = "Section_start.html#start_3">Making LAMMPS</A>
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2011-08-24 05:11:24 +08:00
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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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2011-08-26 00:46:23 +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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2011-08-24 05:11:24 +08:00
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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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2011-08-24 05:11:24 +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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2007-10-03 07:26:51 +08:00
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</P>
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<P>For atom type pairs I,J and I != J, the cutoff distance for the
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<I>coul/cut</I> style can be mixed. The default mix value is <I>geometric</I>.
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See the "pair_modify" command for details.
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</P>
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<P>The <A HREF = "pair_modify.html">pair_modify</A> shift option is not relevant
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for these pair styles.
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</P>
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<P>The <I>coul/long</I> style supports the <A HREF = "pair_modify.html">pair_modify</A>
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table option for tabulation of the short-range portion of the
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long-range Coulombic interaction.
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</P>
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<P>These pair styles do 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>These pair styles write their 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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2007-10-03 07:26:51 +08:00
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<HR>
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<P><B>Restrictions:</B>
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</P>
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2011-08-27 02:53:00 +08:00
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<P>The <I>coul/long</I> style is part of the KSPACE package. It is only
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2007-10-03 07:26:51 +08:00
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enabled if LAMMPS was built with that package (which it is by
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2011-08-26 00:46:23 +08:00
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default). See the <A HREF = "Section_start.html#start_3">Making LAMMPS</A> section
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for more info.
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2007-10-03 07:26:51 +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>, <A HREF = "pair_hybrid.html">pair_style
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hybrid/overlay</A>
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</P>
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<P><B>Default:</B> none
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</P>
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2011-12-13 23:56:58 +08:00
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<HR>
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<A NAME = "Wolf"></A>
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<P><B>(Wolf)</B> D. Wolf, P. Keblinski, S. R. Phillpot, J. Eggebrecht, J Chem
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Phys, 110, 8254 (1999).
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</P>
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2007-10-03 07:26:51 +08:00
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</HTML>
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