forked from lijiext/lammps
133 lines
4.3 KiB
Plaintext
133 lines
4.3 KiB
Plaintext
.. index:: pair_style body
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pair_style body 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 body 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 body 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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Description
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"""""""""""
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Style *body* is for use with body particles and calculates pairwise
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body/body interactions as well as interactions between body and
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point-particles. See :ref:`Section_howto 14 <howto_14>`
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of the manual and the :doc:`body <body>` doc page for more details on
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using body particles.
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This pair style is designed for use with the "nparticle" body style,
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which is specified as an argument to the "atom-style body" command.
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See the :doc:`body <body>` doc page for more details about the body
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styles LAMMPS supports. The "nparticle" style treats a body particle
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as a rigid body composed of N sub-particles.
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The coordinates of a body particle are its center-of-mass (COM). If
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the COMs of a pair of body particles are within the cutoff (global or
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type-specific, as specified above), then all interactions between
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pairs of sub-particles in the two body particles are computed.
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E.g. if the first body particle has 3 sub-particles, and the second
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has 10, then 30 interactions are computed and summed to yield the
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total force and torque on each body particle.
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.. note::
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In the example just described, all 30 interactions are computed
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even if the distance between a particular pair of sub-particles is
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greater than the cutoff. Likewise, no interaction between two body
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particles is computed if the two COMs are further apart than the
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cutoff, even if the distance between some pairs of their sub-particles
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is within the cutoff. Thus care should be used in defining the cutoff
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distances for body particles, depending on their shape and size.
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Similar rules apply for a body particle interacting with a point
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particle. The distance between the two particles is calculated using
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the COM of the body particle and the position of the point particle.
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If the distance is within the cutoff and the body particle has N
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sub-particles, then N interactions with the point particle are
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computed and summed. If the distance is not within the cutoff, no
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interactions between the body and point particle are computed.
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The interaction between two sub-particles, or a sub-particle and point
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particle, or betwee two point particles is computed as a Lennard-Jones
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interaction, using the standard formula
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.. image:: Eqs/pair_lj.jpg
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:align: center
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where Rc is the cutoff. As explained above, an interaction involving
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one or two body sub-particles may be computed even for r > Rc.
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For style *body*\ , the following coefficients must be defined for each
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pair of atoms types via the :doc:`pair_coeff <pair_coeff>` command as in
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the examples above, or in the data file or restart files read by the
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:doc:`read_data <read_data>` or :doc:`read_restart <read_restart>`
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commands:
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* epsilon (energy units)
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* sigma (distance units)
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* cutoff (distance units)
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The last coefficient is optional. If not specified, the global cutoff
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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, 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 *geometric*\ . See the "pair_modify" command for
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details.
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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 BODY package. It is only enabled if LAMMPS
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was built with that package. See the :ref:`Making LAMMPS <start_2_3>` section for more info.
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Defining particles to be bodies so they participate in body/body or
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body/particle interactions requires the use of the :doc:`atom_style body <atom_style>` command.
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Related commands
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""""""""""""""""
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:doc:`pair_coeff <pair_coeff>`, :doc:`fix rigid <fix_rigid>`
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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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