.. index:: pair_style lj/mdf

pair_style lj/mdf command
=========================

pair_style buck/mdf command
===========================

pair_style lennard/mdf command
==============================

Syntax
""""""

.. parsed-literal::

   pair_style style args

* style = *lj/mdf* or *buck/mdf* or *lennard/mdf*
* args = list of arguments for a particular style
.. parsed-literal::

     *lj/mdf* args = cutoff1 cutoff2
       cutoff1 = inner cutoff for the start of the tapering function
       cutoff1 = out cutoff for the end of the tapering function
     *buck/mdf* args = cutoff1 cutoff2
       cutoff1 = inner cutoff for the start of the tapering function
       cutoff1 = out cutoff for the end of the tapering function
     *lennard/mdf* args = cutoff1 cutoff2
       cutoff1 = inner cutoff for the start of the tapering function
       cutoff1 = out cutoff for the end of the tapering function



Examples
""""""""

.. parsed-literal::

   pair_style lj/mdf 2.5 3.0
   pair_coeff * * 1 1
   pair_coeff 1 1 1 1.1 2.8 3.0 3.2

.. parsed-literal::

   pair_style buck 2.5 3.0
   pair_coeff * * 100.0 1.5 200.0
   pair_coeff * * 100.0 1.5 200.0 3.0 3.5

.. parsed-literal::

   pair_style lennard/mdf 2.5 3.0
   pair_coeff * * 1 1
   pair_coeff 1 1 1 1.1 2.8 3.0 3.2

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

The *lj/mdf*\ , *buck/mdf* and *lennard/mdf* compute the standard 12-6
Lennard-Jones and Buckingham potential with the addition of a taper
function that ramps the energy and force smoothly to zero between an
inner and outer cutoff.

.. image:: Eqs/pair_mdf-1.jpg
   :align: center

The tapering, *f(r)*\ , is done by using the Mei, Davenport, Fernando
function :ref:`(Mei) <Mei>`.

.. image:: Eqs/pair_mdf-2.jpg
   :align: center

where

.. image:: Eqs/pair_mdf-3.jpg
   :align: center

Here *r_m* is the inner cutoff radius and *r_cut* is the outer cutoff
radius.


----------


For the *lj/mdf* pair_style, the potential energy, *E(r)*\ , is the
standard 12-6 Lennard-Jones written in the epsilon/sigma form:

.. image:: Eqs/pair_mdf-4.jpg
   :align: center

The following coefficients must be defined for each pair of atoms
types via the 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 commands <read_restart>`, or by mixing as described
below:

* epsilon (energy units)
* sigma (distance units)
* r_m (distance units)
* r_\ *cut* (distance units)


----------


For the *buck/mdf* pair_style, the potential energy, *E(r)*\ , is the
standard Buckingham potential:

.. image:: Eqs/pair_mdf-5.jpg
   :align: center

* A (energy units)
* \rho (distance units)
* C (energy-distance^6 units)
* r_m (distance units)
* r_\ *cut*\ $ (distance units)


----------


For the *lennard/mdf* pair_style, the potential energy, *E(r)*\ , is the
standard 12-6 Lennard-Jones written in the $A/B$ form:

.. image:: Eqs/pair_mdf-6.jpg
   :align: center

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

* A (energy-distance^12 units)
* B (energy-distance^6 units)
* r_m (distance units)
* r_\ *cut* (distance units)


----------


**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 the lj/cut pair styles can be mixed.
The default mix value is *geometric*\ .  See the "pair_modify" command
for details.

All of the *lj/cut* pair styles support the
:doc:`pair_modify <pair_modify>` shift option for the energy of the
Lennard-Jones portion of the pair interaction.

The *lj/cut/coul/long* and *lj/cut/tip4p/long* pair styles support the
:doc:`pair_modify <pair_modify>` table option since they can tabulate
the short-range portion of the long-range Coulombic interaction.

All of the *lj/cut* pair styles support the
:doc:`pair_modify <pair_modify>` tail option for adding a long-range
tail correction to the energy and pressure for the Lennard-Jones
portion of the pair interaction.

All of the *lj/cut* pair styles write their 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.

The *lj/cut* and *lj/cut/coul/long* pair styles support the use of the
*inner*\ , *middle*\ , and *outer* keywords of the :doc:`run_style respa <run_style>` command, meaning the pairwise forces can be
partitioned by distance at different levels of the rRESPA hierarchy.
The other styles only support the *pair* keyword of run_style respa.
See the :doc:`run_style <run_style>` command for details.


----------


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


These pair styles can only be used if LAMMPS was built with the
USER-MISC package.  See the :ref:`Making LAMMPS <start_3>`
section for more info on packages.

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

:doc:`pair_coeff <pair_coeff>`

**Default:** none


----------


.. _Mei:



**(Mei)** Mei, Davenport, Fernando, Phys Rev B, 43 4653 (1991)


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