.. index:: pair_style lj/expand

pair_style lj/expand command
============================

pair_style lj/expand/cuda command
=================================

pair_style lj/expand/gpu command
================================

pair_style lj/expand/omp command
================================

Syntax
""""""

.. parsed-literal::

   pair_style lj/expand cutoff

* cutoff = global cutoff for lj/expand interactions (distance units)

Examples
""""""""

.. parsed-literal::

   pair_style lj/expand 2.5
   pair_coeff * * 1.0 1.0 0.5
   pair_coeff 1 1 1.0 1.0 -0.2 2.0

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

Style *lj/expand* computes a LJ interaction with a distance shifted by
delta which can be useful when particles are of different sizes, since
it is different that using different sigma values in a standard LJ
formula:

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

Rc is the cutoff which does not include the delta distance.  I.e. the
actual force cutoff is the sum of cutoff + delta.

The following coefficients must be defined for each pair of atoms
types via the :doc:`pair_coeff <pair_coeff>` command as in the examples
above, or in the data file or restart files read by the
:doc:`read_data <read_data>` or :doc:`read_restart <read_restart>`
commands, or by mixing as described below:

* epsilon (energy units)
* sigma (distance units)
* delta (distance units)
* cutoff (distance units)

The delta values can be positive or negative.  The last coefficient is
optional.  If not specified, the global LJ cutoff is used.


----------


Styles with a *cuda*\ , *gpu*\ , *intel*\ , *kk*\ , *omp*\ , or *opt* suffix are
functionally the same as the corresponding style without the suffix.
They have been optimized to run faster, depending on your available
hardware, as discussed in :doc:`Section_accelerate <Section_accelerate>`
of the manual.  The accelerated styles take the same arguments and
should produce the same results, except for round-off and precision
issues.

These accelerated styles are part of the USER-CUDA, GPU, USER-INTEL,
KOKKOS, USER-OMP and OPT packages, respectively.  They are only
enabled if LAMMPS was built with those packages.  See the :ref:`Making LAMMPS <start_3>` section for more info.

You can specify the accelerated styles explicitly in your input script
by including their suffix, or you can use the :ref:`-suffix command-line switch <start_7>` when you invoke LAMMPS, or you can
use the :doc:`suffix <suffix>` command in your input script.

See :doc:`Section_accelerate <Section_accelerate>` of the manual for
more instructions on how to use the accelerated styles effectively.


----------


**Mixing, shift, table, tail correction, restart, rRESPA info**\ :

For atom type pairs I,J and I != J, the epsilon, sigma, and shift
coefficients and cutoff distance for this pair style can be mixed.
Shift is always mixed via an *arithmetic* rule.  The other
coefficients are mixed according to the pair_modify mix value.  The
default mix value is *geometric*\ .  See the "pair_modify" command for
details.

This pair style supports the :doc:`pair_modify <pair_modify>` shift
option for the energy of the pair interaction.

The :doc:`pair_modify <pair_modify>` table option is not relevant
for this pair style.

This pair style supports the :doc:`pair_modify <pair_modify>` tail
option for adding a long-range tail correction to the energy and
pressure of the pair interaction.

This pair style writes its information to :doc:`binary restart files <restart>`, so pair_style and pair_coeff commands do not need
to be specified in an input script that reads a restart file.

This pair style can only be used via the *pair* keyword of the
:doc:`run_style respa <run_style>` command.  It does not support the
*inner*\ , *middle*\ , *outer* keywords.


----------


Restrictions
""""""""""""
 none

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

:doc:`pair_coeff <pair_coeff>`

**Default:** none


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