forked from lijiext/lammps
121 lines
4.7 KiB
HTML
121 lines
4.7 KiB
HTML
|
<HTML>
|
||
|
|
<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>
|
||
|
|
</CENTER>
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
<HR>
|
||
|
|
|
||
|
|
<H3>pair_style tri command
|
||
|
|
</H3>
|
||
|
|
<P><B>Syntax:</B>
|
||
|
|
</P>
|
||
|
|
<PRE>pair_style tri cutoff
|
||
|
|
</PRE>
|
||
|
|
<P>cutoff = global cutoff for interactions (distance units)
|
||
|
|
</P>
|
||
|
|
<P><B>Examples:</B>
|
||
|
|
</P>
|
||
|
|
<PRE>pair_style tri 3.0
|
||
|
|
pair_coeff * * 1.0 1.0
|
||
|
|
pair_coeff 1 1 1.0 1.5 2.5
|
||
|
|
</PRE>
|
||
|
|
<P><B>Description:</B>
|
||
|
|
</P>
|
||
|
|
<P>Style <I>tri</I> treats particles which are triangles as a set of small
|
||
|
|
spherical particles that tile the triangle surface as explained below.
|
||
|
|
Interactions between two triangles, each with N1 and N2 spherical
|
||
|
|
particles, are calculated as the pairwise sum of N1*N2 Lennard-Jones
|
||
|
|
interactions. Interactions between a triangle with N spherical
|
||
|
|
particles and a point particle are treated as the pairwise sum of N
|
||
|
|
Lennard-Jones interactions. See the <A HREF = "pair_lj.html">pair_style lj/cut</A>
|
||
|
|
doc page for the definition of Lennard-Jones interactions.
|
||
|
|
</P>
|
||
|
|
<P>The cutoff distance for an interaction between 2 triangles, or between
|
||
|
|
a triangle and a point particle, is calculated from the position of
|
||
|
|
the triangle (its centroid), not between pairs of individual spheres
|
||
|
|
comprising the triangle. Thus an interaction is either calculated in
|
||
|
|
its entirety or not at all.
|
||
|
|
</P>
|
||
|
|
<P>The set of non-overlapping spherical particles that represent a
|
||
|
|
triangle, for purposes of this pair style, are generated in the
|
||
|
|
following manner. Assume the triangle is of type I, and sigma_II has
|
||
|
|
been specified. We want a set of spheres with centers in the plane of
|
||
|
|
the triangle, none of them larger in diameter than sigma_II, which
|
||
|
|
completely cover the triangle's area, but with minimial overlap and a
|
||
|
|
minimal total number of spheres. This is done in a recursive manner.
|
||
|
|
Place a sphere at the centroid of the original triangle. Calculate
|
||
|
|
what diameter it must have to just cover all 3 corner points of the
|
||
|
|
triangle. If that diameter is equal to or smaller than sigma_II, then
|
||
|
|
include a sphere of the calculated diameter in the set of covering
|
||
|
|
spheres. It the diameter is larger than sigma_II, then split the
|
||
|
|
triangle into 2 triangles by bisecting its longest side. Repeat the
|
||
|
|
process on each sub-triangle, recursing as far as needed to generate a
|
||
|
|
set of covering spheres. When finished, the original criteria are
|
||
|
|
met, and the set of covering spheres shoule be near minimal in number
|
||
|
|
and overlap, at least for input triangles with a reasonable
|
||
|
|
aspect-ratio.
|
||
|
|
</P>
|
||
|
|
<P>The LJ interaction between 2 spheres on different triangles of types
|
||
|
|
I,J is computed with an arithmetic mixing of the sigma values of the 2
|
||
|
|
spheres and using the specified epsilon value for I,J atom types.
|
||
|
|
Note that because the sigma values for triangles spheres is computed
|
||
|
|
using only sigma_II values, specific to the triangles's type, this
|
||
|
|
means that any specified sigma_IJ values (for I != J) are effectively
|
||
|
|
ignored.
|
||
|
|
</P>
|
||
|
|
<P>For style <I>tri</I>, the following coefficients must be defined for each
|
||
|
|
pair of atoms types via the <A HREF = "pair_coeff.html">pair_coeff</A> command as in
|
||
|
|
the examples above, or in the data file or restart files read by the
|
||
|
|
<A HREF = "read_data.html">read_data</A> or <A HREF = "read_restart.html">read_restart</A>
|
||
|
|
commands:
|
||
|
|
</P>
|
||
|
|
<UL><LI>epsilon (energy units)
|
||
|
|
<LI>sigma (distance units)
|
||
|
|
<LI>cutoff (distance units)
|
||
|
|
</UL>
|
||
|
|
<P>The last coefficient is optional. If not specified, the global cutoff
|
||
|
|
is used.
|
||
|
|
</P>
|
||
|
|
<HR>
|
||
|
|
|
||
|
|
<P><B>Mixing, shift, table, tail correction, restart, rRESPA info</B>:
|
||
|
|
</P>
|
||
|
|
<P>For atom type pairs I,J and I != J, the epsilon and sigma coefficients
|
||
|
|
and cutoff distance for all of this pair style can be mixed. The
|
||
|
|
default mix value is <I>geometric</I>. See the "pair_modify" command for
|
||
|
|
details.
|
||
|
|
</P>
|
||
|
|
<P>This pair style does not support the <A HREF = "pair_modify.html">pair_modify</A>
|
||
|
|
shift, table, and tail options.
|
||
|
|
</P>
|
||
|
|
<P>This pair style does not write its information to <A HREF = "restart.html">binary restart
|
||
|
|
files</A>.
|
||
|
|
</P>
|
||
|
|
<P>This pair style can only be used via the <I>pair</I> keyword of the
|
||
|
|
<A HREF = "run_style.html">run_style respa</A> command. It does not support the
|
||
|
|
<I>inner</I>, <I>middle</I>, <I>outer</I> keywords.
|
||
|
|
</P>
|
||
|
|
<HR>
|
||
|
|
|
||
|
|
<P><B>Restrictions:</B>
|
||
|
|
</P>
|
||
|
|
<P>This style is part of the ASPHERE package. It is only enabled if
|
||
|
|
LAMMPS was built with that package. See the <A HREF = "Section_start.html#2_3">Making
|
||
|
|
LAMMPS</A> section for more info.
|
||
|
|
</P>
|
||
|
|
<P>Defining particles to be triangles so they participate in tri/tri or
|
||
|
|
tri/particle interactions requires the use the <A HREF = "atom_style.html">atom_style
|
||
|
|
tri</A> command.
|
||
|
|
</P>
|
||
|
|
<P><B>Related commands:</B>
|
||
|
|
</P>
|
||
|
|
<P><A HREF = "pair_coeff.html">pair_coeff</A>
|
||
|
|
</P>
|
||
|
|
<P><B>Default:</B> none
|
||
|
|
</P>
|
||
|
|
</HTML>
|