forked from lijiext/lammps
145 lines
5.9 KiB
HTML
145 lines
5.9 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 tri/lj command
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</H3>
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<H3>pair_style tri/lj/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 tri/lj cutoff
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</PRE>
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<P>cutoff = global cutoff for interactions (distance units)
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</P>
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<P><B>Examples:</B>
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</P>
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<PRE>pair_style tri/lj 3.0
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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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</PRE>
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<P><B>Description:</B>
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</P>
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<P>Style <I>tri/lj</I> treats particles which are triangles as a set of small
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spherical particles that tile the triangle surface as explained below.
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Interactions between two triangles, each with N1 and N2 spherical
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particles, are calculated as the pairwise sum of N1*N2 Lennard-Jones
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interactions. Interactions between a triangle with N spherical
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particles and a point particle are treated as the pairwise sum of N
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Lennard-Jones interactions. See the <A HREF = "pair_lj.html">pair_style lj/cut</A>
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doc page for the definition of Lennard-Jones interactions.
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</P>
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<P>The cutoff distance for an interaction between 2 triangles, or between
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a triangle and a point particle, is calculated from the position of
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the triangle (its centroid), not between pairs of individual spheres
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comprising the triangle. Thus an interaction is either calculated in
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its entirety or not at all.
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</P>
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<P>The set of non-overlapping spherical particles that represent a
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triangle, for purposes of this pair style, are generated in the
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following manner. Assume the triangle is of type I, and sigma_II has
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been specified. We want a set of spheres with centers in the plane of
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the triangle, none of them larger in diameter than sigma_II, which
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completely cover the triangle's area, but with minimial overlap and a
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minimal total number of spheres. This is done in a recursive manner.
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Place a sphere at the centroid of the original triangle. Calculate
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what diameter it must have to just cover all 3 corner points of the
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triangle. If that diameter is equal to or smaller than sigma_II, then
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include a sphere of the calculated diameter in the set of covering
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spheres. It the diameter is larger than sigma_II, then split the
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triangle into 2 triangles by bisecting its longest side. Repeat the
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process on each sub-triangle, recursing as far as needed to generate a
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set of covering spheres. When finished, the original criteria are
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met, and the set of covering spheres shoule be near minimal in number
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and overlap, at least for input triangles with a reasonable
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aspect-ratio.
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</P>
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<P>The LJ interaction between 2 spheres on different triangles of types
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I,J is computed with an arithmetic mixing of the sigma values of the 2
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spheres and using the specified epsilon value for I,J atom types.
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Note that because the sigma values for triangles spheres is computed
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using only sigma_II values, specific to the triangles's type, this
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means that any specified sigma_IJ values (for I != J) are effectively
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ignored.
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</P>
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<P>For style <I>tri/lj</I>, the following coefficients must be defined for
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each pair of atoms types via the <A HREF = "pair_coeff.html">pair_coeff</A> command
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as in the examples above, or in the data file or restart files read by
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the <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>epsilon (energy units)
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<LI>sigma (distance units)
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<LI>cutoff (distance units)
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</UL>
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<P>The last coefficient is optional. If not specified, the global cutoff
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is 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 and sigma coefficients
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and cutoff distance for all of this pair style can be mixed. 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 does not support the <A HREF = "pair_modify.html">pair_modify</A>
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shift, table, and tail options.
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</P>
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<P>This pair style does not write its information to <A HREF = "restart.html">binary restart
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files</A>.
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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>
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</P>
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<P>This style is part of the ASPHERE package. It is only enabled if
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LAMMPS was built with that package. See the <A HREF = "Section_start.html#2_3">Making
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LAMMPS</A> section for more info.
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</P>
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<P>Defining particles to be triangles so they participate in tri/tri or
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tri/particle interactions requires the use the <A HREF = "atom_style.html">atom_style
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tri</A> command.
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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_line_lj.html">pair_style line/lj</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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