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183 lines
6.9 KiB
HTML
183 lines
6.9 KiB
HTML
<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 nm/cut command
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</H3>
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<H3>pair_style nm/cut/coul/cut command
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</H3>
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<H3>pair_style nm/cut/coul/long command
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</H3>
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<H3>pair_style nm/cut/omp command
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</H3>
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<H3>pair_style nm/cut/coul/cut/omp command
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</H3>
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<H3>pair_style nm/cut/coul/long/omp 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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<UL><LI>style = <I>nm/cut</I> or <I>nm/cut/coul/cut</I> or <I>nm/cut/coul/long</I>
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<LI>args = list of arguments for a particular style
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<PRE> <I>nm/cut</I> args = cutoff
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cutoff = global cutoff for Pair interactions (distance units)
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<I>nm/cut/coul/cut</I> args = cutoff (cutoff2)
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cutoff = global cutoff for Pair (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>nm/cut/coul/long</I> args = cutoff (cutoff2)
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cutoff = global cutoff for Pair (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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</UL>
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<P><B>Examples:</B>
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</P>
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<PRE>pair_style nm/cut 12.0
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pair_coeff * * 0.01 5.4 8.0 7.0
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pair_coeff 1 1 0.01 4.4 7.0 6.0
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</PRE>
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<PRE>pair_style nm/cut/coul/cut 12.0 15.0
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pair_coeff * * 0.01 5.4 8.0 7.0
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pair_coeff 1 1 0.01 4.4 7.0 6.0
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</PRE>
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<PRE>pair_style nm/cut/coul/long 12.0 15.0
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pair_coeff * * 0.01 5.4 8.0 7.0
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pair_coeff 1 1 0.01 4.4 7.0 6.0
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>Style <I>nm</I> computes site-site interactions based on the N-M potential
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by <A HREF = "#Clarke">Clarke</A>, mainly used for ionic liquids. A site can
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represent a single atom or a united-atom site. The energy of an
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interaction has the following form:
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</P>
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<CENTER><IMG SRC = "Eqs/pair_nm.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>nm/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 NM and
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Coulombic terms. If two cutoffs are specified, they are used as
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cutoffs for the NM and Coulombic terms respectively.
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</P>
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<P>Styles <I>nm/cut/coul/long</I> compute the same
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Coulombic interactions as style <I>nm/cut/coul/cut</I> except that an
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additional damping factor is applied to the Coulombic term so it can
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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>For all of the <I>nm</I> pair styles, the following coefficients must
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be defined for each pair of atoms types
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via the <A HREF = "pair_coeff.html">pair_coeff</A> command as in the
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examples 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.
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</P>
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<UL><LI>E0 (energy units)
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<LI>r0 (distance units)
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<LI>n (unitless)
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<LI>m (unitless)
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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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NM 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 NM
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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 NM and Coulombic cutoffs for this
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type pair. You cannot specify 2 cutoffs for style <I>nm</I>, since it
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has no Coulombic terms.
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</P>
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<P>For <I>nm/cut/coul/long</I> only the NM cutoff can be specified since a
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Coulombic cutoff cannot be specified for an individual I,J type pair.
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All type pairs use the same global Coulombic cutoff specified in the
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pair_style command.
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</P>
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<HR>
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<P><B>Mixing, shift, table, tail correction, restart, rRESPA info</B>:
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</P>
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<P>These pair styles do not support mixing. Thus, coefficients for all
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I,J pairs must be specified explicitly.
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</P>
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<P>All of the <I>nm</I> pair styles supports the
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<A HREF = "pair_modify.html">pair_modify</A> shift option for the energy of the pair
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interaction.
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</P>
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<P>The <I>nm/cut/coul/long</I> pair styles support the
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<A HREF = "pair_modify.html">pair_modify</A> table option since they can tabulate
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the short-range portion of the long-range Coulombic interaction.
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</P>
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<P>All of the <I>nm</I> pair styles support the <A HREF = "pair_modify.html">pair_modify</A>
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tail option for adding a long-range tail correction to the energy and
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pressure for the NM portion of the pair interaction.
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</P>
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<P>All of the <I>nm</I> 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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<P>All of the <I>nm</I> pair styles can only be used via the <I>pair</I> keyword of
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the <A HREF = "run_style.html">run_style respa</A> command. They do not support the
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<I>inner</I>, <I>middle</I>, <I>outer</I> keywords.
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</P>
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<HR>
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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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</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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by including their suffix, or you can use the <A HREF = "Section_start.html#start_7">-suffix command-line
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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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<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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</P>
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<P><B>Restrictions:</B>
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</P>
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<P>These pair styles are part of the MISC package. It is only enabled if
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LAMMPS was built with that package. See the <A HREF = "Section_start.html#start_3">Making
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LAMMPS</A> 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 = "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 = "Clarke"></A>
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<P><B>(Clarke)</B> Clarke and Smith, J Chem Phys, 84, 2290 (1986).
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</P>
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</HTML>
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