lammps/doc/pair_line_lj.txt

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:line

pair_style line command :h3

[Syntax:]

pair_style line cutoff :pre

cutoff = global cutoff for interactions (distance units)

[Examples:]

pair_style line 3.0
pair_coeff * * 1.0 1.0
pair_coeff 1 1 1.0 1.5 2.5 :pre

[Description:]

Style {line} treats particles which are line segments as a set of
small spherical particles that tile the line segment length as
explained below.  Interactions between two line segments, each with N1
and N2 spherical particles, are calculated as the pairwise sum of
N1*N2 Lennard-Jones interactions.  Interactions between a line segment
with N spherical particles and a point particle are treated as the
pairwise sum of N Lennard-Jones interactions.  See the "pair_style
lj/cut"_pair_lj.html doc page for the definition of Lennard-Jones
interactions.

The cutoff distance for an interaction between 2 line segments, or
between a line segment and a point particle, is calculated from the
position of the line segment (its center), not between pairs of
individual spheres comprising the line segment.  Thus an interaction
is either calculated in its entirety or not at all.

The set of non-overlapping spherical particles that represent a line
segment, for purposes of this pair style, are generated in the
following manner.  Their size is a function of the line segment length
and the specified sigma for that particle type.  If a line segment has
a length L and is of type I, then the number of spheres N that
represent the segment is calculated as N = L/sigma_II, rounded up to
an integer value.  Thus if L is not evenly divisibly by sigam_II, N is
incremented to include one extra sphere.  In this case, the spheres
must be slightly smaller than sigma_II so as not to overlap, so a new
sigma-prime is chosen as the sphere diameter, such that L/N =
sigma-prime.  Thus the line segment interacts with other segments or
point particles as a collection of N spheres of diameter sigma-prime,
evenly spaced along the line segment, so as to exactly cover its
length.

The LJ interaction between 2 spheres on different line segments 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 line segment spheres is
computed using only sigma_II values, specific to the line segment's
type, this means that any specified sigma_IJ values (for I != J) are
effectively ignored.

For style {line}, the following coefficients must be defined for each
pair of atoms types via the "pair_coeff"_pair_coeff.html command as in
the examples above, or in the data file or restart files read by the
"read_data"_read_data.html or "read_restart"_read_restart.html
commands:

epsilon (energy units)
sigma (distance units)
cutoff (distance units) :ul

The last coefficient is optional.  If not specified, the global cutoff
is used.

:line

[Mixing, shift, table, tail correction, restart, rRESPA info]:

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 {geometric}.  See the "pair_modify" command for
details.

This pair style does not support the "pair_modify"_pair_modify.html
shift, table, and tail options.

This pair style does not write its information to "binary restart
files"_restart.html.

This pair style can only be used via the {pair} keyword of the
"run_style respa"_run_style.html command.  It does not support the
{inner}, {middle}, {outer} keywords.

:line

[Restrictions:]

This style is part of the ASPHERE package.  It is only enabled if
LAMMPS was built with that package.  See the "Making
LAMMPS"_Section_start.html#2_3 section for more info.

Defining particles to be line segments so they participate in
line/line or line/particle interactions requires the use the
"atom_style line"_atom_style.html command.

[Related commands:]

"pair_coeff"_pair_coeff.html

[Default:] none