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doc/html/_sources/pair_line_lj.txt
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doc/html/_sources/pair_line_lj.txt
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.. index:: pair_style line/lj
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pair_style line/lj command
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==========================
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Syntax
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""""""
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.. parsed-literal::
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pair_style line/lj cutoff
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cutoff = global cutoff for interactions (distance units)
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Examples
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""""""""
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.. parsed-literal::
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pair_style line/lj 3.0
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pair_coeff * * 1.0 1.0 1.0 0.8 1.12
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pair_coeff 1 2 1.0 2.0 1.0 1.5 1.12 5.0
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pair_coeff 1 2 1.0 0.0 1.0 1.0 2.5
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Description
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"""""""""""
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Style *line/lj* treats particles which are line segments as a set of
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small spherical particles that tile the line segment length as
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explained below. Interactions between two line segments, each with N1
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and N2 spherical particles, are calculated as the pairwise sum of
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N1*N2 Lennard-Jones interactions. Interactions between a line segment
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with N spherical particles and a point particle are treated as the
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pairwise sum of N Lennard-Jones interactions. See the :doc:`pair_style lj/cut <pair_lj>` doc page for the definition of Lennard-Jones
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interactions.
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The set of non-overlapping spherical sub-particles that represent a
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line segment are generated in the following manner. Their size is a
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function of the line segment length and the specified sub-particle
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size for that particle type. If a line segment has a length L and is
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of type I, then the number of spheres N that represent the segment is
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calculated as N = L/sizeI, rounded up to an integer value. Thus if L
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is not evenly divisibly by sizeI, N is incremented to include one
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extra sphere. The centers of the spheres are spaced equally along the
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line segment. Imagine N+1 equally-space points, which include the 2
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end points of the segment. The sphere centers are halfway between
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each pair of points.
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The LJ interaction between 2 spheres on different line segments (or a
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sphere on a line segment and a point particles) is computed with
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sub-particle epsilon, sigma, and cutoff values that are set by the
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pair_coeff command, as described below. If the distance bewteen the 2
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spheres is greater than the sub-particle cutoff, there is no
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interaction. This means that some pairs of sub-particles on 2 line
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segments may interact, but others may not.
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For purposes of creating the neighbor list for pairs of interacting
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line segments or lines/point particles, a regular particle-particle
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cutoff is used, as defined by the *cutoff* setting above in the
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pair_style command or overridden with an optional argument in the
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pair_coeff command for a type pair as discussed below. The distance
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between the centers of 2 line segments, or the center of a line
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segment and a point particle, must be less than this distance (plus
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the neighbor skin; see the `neighbor <neighbor>`_ command), for the pair
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of particles to be included in the neighbor list.
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.. note::
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This means that a too-short value for the *cutoff* setting can
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exclude a pair of particles from the neighbor list even if pairs of
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their sub-particle spheres would interact, based on the sub-particle
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cutoff specified in the pair_coeff command. E.g. sub-particles at the
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ends of the line segments that are close to each other. Which may not
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be what you want, since it means the ends of 2 line segments could
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pass through each other. It is up to you to specify a *cutoff*
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setting that is consistent with the length of the line segments you
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are using and the sub-particle cutoff settings.
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For style *line/lj*\ , the following coefficients must be defined for
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each pair of atom types via the :doc:`pair_coeff <pair_coeff>` 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 :doc:`read_data <read_data>` or :doc:`read_restart <read_restart>`
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commands:
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* sizeI (distance units)
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* sizeJ (distance units)
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* epsilon (energy units)
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* sigma (distance units)
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* subcutoff (distance units)
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* cutoff (distance units)
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The *sizeI* and *sizeJ* coefficients are the sub-particle sizes for
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line particles of type I and type J. They are used to define the N
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sub-particles per segment as described above. These coefficients are
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actually stored on a per-type basis. Thus if there are multiple
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pair_coeff commmands that involve type I, as either the first or
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second atom type, you should use consistent values for sizeI or sizeJ
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in all of them. If you do not do this, the last value specified for
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sizeI will apply to all segments of type I. If typeI or typeJ refers
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to point particles, the corresponding sizeI or sizeJ is ignored; it
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can be set to 0.0.
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The *epsilon*\ , *sigma*\ , and *subcutoff* coefficients are used to
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compute an LJ interactions between a pair of sub-particles on 2 line
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segments (of type I and J), or between a sub particle/point particle
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pair. As discussed above, the *subcutoff* and *cutoff* params are
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different. The latter is only used for building the neighbor list
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when the distance between centers of two line segments or one segment
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and a point particle is calculated.
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The *cutoff* coefficient is optional. If not specified, the global
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cutoff is used.
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----------
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**Mixing, shift, table, tail correction, restart, rRESPA info**\ :
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For atom type pairs I,J and I != J, coeffiecients must be specified.
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No default mixing rules are used.
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This pair style does not support the :doc:`pair_modify <pair_modify>`
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shift, table, and tail options.
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This pair style does not write its information to :doc:`binary restart files <restart>`.
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This pair style can only be used via the *pair* keyword of the
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:doc:`run_style respa <run_style>` command. It does not support the
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*inner*\ , *middle*\ , *outer* keywords.
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----------
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Restrictions
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""""""""""""
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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 :ref:`Making LAMMPS <2_3>` section for more info.
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Defining particles to be line segments so they participate in
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line/line or line/particle interactions requires the use the
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:doc:`atom_style line <atom_style>` command.
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Related commands
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""""""""""""""""
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:doc:`pair_coeff <pair_coeff>`, :doc:`pair_style tri/lj <pair_tri_lj>`
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**Default:** none
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.. _lws: http://lammps.sandia.gov
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.. _ld: Manual.html
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.. _lc: Section_commands.html#comm
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