forked from lijiext/lammps
130 lines
4.8 KiB
HTML
130 lines
4.8 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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</CENTER>
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<HR>
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<H3>pair_style lj/smooth command
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</H3>
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<H3>pair_style lj/smooth/cuda command
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</H3>
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<H3>pair_style lj/smooth/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 lj/smooth Rin Rc
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</PRE>
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<UL><LI>Rin = inner cutoff beyond which force smoothing will be applied (distance units)
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<LI>Rc = outer cutoff for lj/smooth interactions (distance units)
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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 lj/smooth 8.0 10.0
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pair_coeff * * 10.0 1.5
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pair_coeff 1 1 20.0 1.3 7.0 9.0
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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>lj/smooth</I> computes a LJ interaction with a force smoothing
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applied between the inner and outer cutoff.
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</P>
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<CENTER><IMG SRC = "Eqs/pair_lj_smooth.jpg">
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</CENTER>
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<P>The polynomial coefficients C1, C2, C3, C4 are computed by LAMMPS to
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cause the force to vary smoothly from the inner cutoff Rin to the
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outer cutoff Rc.
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</P>
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<P>At the inner cutoff the force and its 1st derivative
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will match the unsmoothed LJ formula. At the outer cutoff the force
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and its 1st derivative will be 0.0. The inner cutoff cannot be 0.0.
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</P>
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<P>IMPORTANT NOTE: this force smoothing causes the energy to be
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discontinuous both in its values and 1st derivative. This can lead to
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poor energy conservation and may require the use of a thermostat.
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Plot the energy and force resulting from this formula via the
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<A HREF = "pair_write.html">pair_write</A> command to see the effect.
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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>epsilon (energy units)
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<LI>sigma (distance units)
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<LI>innner (distance units)
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<LI>outer (distance units)
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</UL>
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<P>The last 2 coefficients are optional inner and outer cutoffs. If not
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specified, the global values for Rin and Rc are used.
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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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<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>For atom type pairs I,J and I != J, the epsilon, sigma, Rin
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coefficients and the cutoff distance for this pair style can be mixed.
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Rin is a cutoff value and is mixed like the cutoff. The other
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coefficients are mixed according to the pair_modify mix option. The
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default mix value is <I>geometric</I>. See the "pair_modify" command for
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details.
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</P>
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<P>This pair style supports the <A HREF = "pair_modify.html">pair_modify</A> shift
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option for the energy of the pair interaction.
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</P>
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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, since the energy of the pair interaction is smoothed to 0.0
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at the cutoff.
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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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<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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<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><B>Restrictions:</B> none
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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_lj_smooth_linear.html">pair
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lj/smooth/linear</A>
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</P>
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<P><B>Default:</B> none
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</P>
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</HTML>
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