.. index:: pair_style born/coul/long/cs

pair_style born/coul/long/cs command
====================================

pair_style buck/coul/long/cs command
====================================

Syntax
""""""

.. parsed-literal::

   pair_style style args

* style = *born/coul/long/cs* or *buck/coul/long/cs*
* args = list of arguments for a particular style

.. parsed-literal::

     *born/coul/long/cs* args = cutoff (cutoff2)
       cutoff = global cutoff for non-Coulombic (and Coulombic if only 1 arg) (distance units)
       cutoff2 = global cutoff for Coulombic (optional) (distance units)
     *buck/coul/long/cs* args = cutoff (cutoff2)
       cutoff = global cutoff for Buckingham (and Coulombic if only 1 arg) (distance units)
       cutoff2 = global cutoff for Coulombic (optional) (distance units)

Examples
""""""""

.. parsed-literal::

   pair_style born/coul/long/cs 10.0 8.0
   pair_coeff 1 1 6.08 0.317 2.340 24.18 11.51

.. parsed-literal::

   pair_style buck/coul/long/cs 10.0
   pair_style buck/coul/long/cs 10.0 8.0
   pair_coeff * * 100.0 1.5 200.0
   pair_coeff 1 1 100.0 1.5 200.0 9.0

Description
"""""""""""

These pair styles are designed to be used with the adiabatic
core/shell model of :ref:`(Mitchell and Finchham) <MitchellFinchham>`.  See
:ref:`Section_howto 25 <howto_25>` of the manual for an
overview of the model as implemented in LAMMPS.

These pair styles are identical to the :doc:`pair_style born/coul/long <pair_born>` and :doc:`pair_style buck/coul/long <pair_buck>` styles, except they correctly treat the
special case where the distance between two charged core and shell
atoms in the same core/shell pair approach r = 0.0.  This needs
special treatment when a long-range solver for Coulombic interactions
is also used, i.e. via the :doc:`kspace_style <kspace_style>` command.

More specifically, the short-range Coulomb interaction between a core
and its shell should be turned off using the
:doc:`special_bonds <special_bonds>` command by setting the 1-2 weight
to 0.0, which works because the core and shell atoms are bonded to
each other.  This induces a long-range correction approximation which
fails at small distances (~< 10e-8). Therefore, the Coulomb term which
is used to calculate the correction factor is extended by a minimal
distance (r_min = 1.0-6) when the interaction between a core/shell
pair is treated, as follows

.. image:: Eqs/pair_cs.jpg
   :align: center

where C is an energy-conversion constant, Qi and Qj are the charges on
the core and shell, epsilon is the dielectric constant and r_min is the
minimal distance.

Restrictions
""""""""""""


These pair styles are part of the CORESHELL package.  They are only
enabled if LAMMPS was built with that package.  See the :ref:`Making LAMMPS <start_3>` section for more info.

Related commands
""""""""""""""""

:doc:`pair_coeff <pair_coeff>`, :doc:`pair_style born <pair_born>`, 
:doc:`pair_style buck <pair_buck>`

**Default:** none


----------


.. _MitchellFinchham:



**(Mitchell and Finchham)** Mitchell, Finchham, J Phys Condensed Matter,
5, 1031-1038 (1993).


.. _lws: http://lammps.sandia.gov
.. _ld: Manual.html
.. _lc: Section_commands.html#comm